This is taken from the Tweakguides Nvidia Forceware Tweakguide which can be found here:
Link Removed
Old Driver Removal
Now we move on to the simplest, and yet most commonly mishandled part of using graphics drivers - the removal of previous Nvidia graphics drivers. To do this successfully, you need to follow some simple steps which will help guarantee that your installation of the drivers is 'clean', and leads to trouble-free performance. I particularly recommend this procedure if you are experiencing graphical corruption, performance issues, or strange behavior. To completely remove your existing graphics drivers and all traces of them from your system do the following:
1. Uninstall any existing graphics drivers. To do this, go to Control Panel>Add or Remove Programs in XP or Control Panel>Programs and Features in Vista. Select the 'Nvidia Drivers' (or similar) item if available and click the Change/Remove or Uninstall button and follow the prompts, rebooting as required. If you happen to have any other graphics drivers left over from previous hardware, such as ATI graphics drivers, uninstall them from here as well. If you have an Nvidia-based motherboard, when uninstalling the Nvidia drivers you will have to specifically select the 'Remove only the following' item, then only select the 'Nvidia Display Drivers' box. If you cannot find any Nvidia display-related entries (e.g. a fresh install of Windows), you are probably using the default Windows graphics drivers, which means you can skip to the New Driver Installation section further below.
Note that if available, you may wish to save your settings under a custom Profile (see further above) before you uninstall the Forceware drivers. Note further that In more recent Nvidia drivers there will also be an 'Nvidia PhysX' component, and even a 'Nvidia Stereoscopic 3D driver' component. You should uninstall both of these as well before installing newer drivers to prevent any problems.
Prior to the next step, you may hear some people recommending that you reboot Windows into Safe Mode before continuing installation. You can do this if you wish - see the TweakGuides Tweaking Companion for details of how to enter Safe Mode, and what exactly it does. However this is almost always unnecessary; you do not need to enter Safe Mode to install/uninstall drivers properly. Only if you're having serious problems which nothing else resolves should you use the Safe Mode method.
2. When you reboot, you will find Windows may detect your graphics card as a new device and attempt to find appropriate drivers for your card. Cancel out of all such attempts. If you can't then don't worry about it, but it is preferable if you can prevent this from occurring.
3. This step is optional, however it is strongly recommended if you are either (a) downgrading your Forceware drivers to an older version, or (b) experiencing problems and want to ensure you have a complete 'clean' install of the Forceware drivers. Basically the aim is to find all the individual Nvidia graphics driver files and remove them manually. Note that if you have an Nvidia nForce motherboard, it is recommended that you undertake this step with great caution, as you may accidentally delete Nvidia driver files which relate to your motherboard and not the graphics card. The instructions differ based on your OS:
Automated Removal
For less advanced users, or for those who want to take less of a risk, you can remove older driver files using the free and fully automated Driver Sweeper utility.
Manual Removal
If you are still experiencing problems after using the automated method, or you want to be certain you've removed all driver debris, use the manual method below, though it carries extra risks:
Windows XP: For nForce users, the only file you can safely delete is nv4_disp.dll which relates to the graphics driver - skip to step 4 below after that. For all non-nForce users, to manually delete the Forceware drivers go to your \Windows\System32 and \Windows\System32\Drivers directories, and find and delete all files beginning with 'NV...'. You may notice that some of these files keep recreating themselves - don't worry, these are just the default XP Nvidia drivers which are protected and can't be permanently deleted. Just delete all the Nvidia driver files and let Windows decide which default files the system should keep. Alternatively you can use the Windows Search function (Start>Search), with the search string NV*.* to make searching and deletion faster. Importantly however, do not delete the files under the \ServicePackFiles or \Lastgood directories, or under any game or application-specific directories. Just stick to files found under the two directories mentioned earlier.
Windows Vista: See the 'Viewing, Updating or Uninstalling Drivers' section of the Windows Drivers chapter of the TweakGuides Tweaking Companion for Windows Vista. It is trickier to manually remove driver traces in Vista, so you must read the instructions carefully to see how it's done. Generally speaking manual driver removal in Vista shouldn't be required unless you're experiencing problems.
Note: If you want to know the exact filenames of all the Nvidia graphics driver files in use on your system, prior to uninstalling the drivers open the Forceware Control Panel and click the 'System Information' link in the bottom left corner of the new Forceware CP. Under the Components tab of the box which opens you can see all the individual filenames and the functionality they relate to. Make a note of these and you can then search for and remove any that are left after you've uninstalled the drivers.
Finally, make sure you delete the entire program folder(s) where you installed the Forceware drivers. The default install location is \NVIDIA but if you chose another location when installing, go there and delete the folder and all its contents.
4. This step is completely optional, but again it is recommended if you want to ensure a totally 'clean' install, especially if you are experiencing graphics-related problems. See the Windows Registry chapter of the TweakGuides Tweaking Companion for the relevant tools you can use to do this. If you're using the Windows Registry Editor to manually delete registry entries - which is recommended only for more advanced users - go to Start>Run and type "RegEdit" (without quotes) and press Enter. Then go to the HKEY_LOCAL_MACHINE key, select the 'Software' subkey, and scroll down to the 'Nvidia Corporation' entry, and underneath you should find a 'Global' entry. Right-Click on this 'Global' key and select Delete to remove it. You may also want to delete the 'Installer' and 'NVControlPanel' keys. Do not remove any other items.
That should remove all the main bits and pieces of old Nvidia graphics drivers and Control Panels which have been installed on your system previously. Of course the quickest method is to just uninstall the Nvidia Display Driver item in Add/Remove Programs or Programs and Features under the Control Panel, but as I said, if you have a history of graphical problems, if you've installed multiple versions of the Forceware drivers without a clean out, or if you are reverting to an older version of the Forceware drivers from a newer one, I strongly suggest you follow all four steps above at least once.
New Driver Installation
Once you've uninstalled any old Nvidia graphics drivers, there is nothing tricky or difficult about installing the new Forceware drivers. The whole process is simple, but here it is in case you want to be 100% certain it's being done right:
1. Once you've downloaded the latest Official Forceware driver package, simply double-click on it to launch the Nvidia driver installation wizard.
2. When the driver package prompts you for a directory to install the Forceware drivers, it is important to note that this directory is just the place where the files will be temporarily unzipped for installation purposes. It is not where the final drivers will be installed. You can leave the default location shown, but I personally recommend you specify an empty folder of your own choosing. In any case make a note of the directory name, as after installation you can safely delete this directory and its contents - see the Tidying Up section on the next page.
3. Follow the remaining prompts and during the installation process reboot as often as you are prompted, since this is also an important step in making sure Windows has a chance to replace system files which are currently in use. As noted above, you do not need to enter Safe Mode in Windows to properly install/uninstall drivers.
If you want to install an unofficial or beta Forceware driver set, and there is no single executable driver package, you will have to manually install the driver file. To do this, go to the Windows Control Panel>System>Hardware>Device Manager in XP or Control Panel>Device Manager in Vista and under the 'Display Adapters' category, double-click on your particular graphics card. Go to the Driver tab and click the 'Update Driver' option, then select 'Install from a list or specific location' and click Next. Then select 'Don't search, I will choose the driver to install' and click Next. On the next screen click the 'Have Disk' button and Browse to the directory where the new Forceware driver files are located, and find the appropriate .INF file.
Once the above is done, your new Forceware drivers should be installed and your system should be fully functional. Test out a few of your games to see if there are any obvious issues or glitches. If available, you can also load up your Forceware Control Panel settings from any pre-saved Profiles you may have - see the Profiles section further above.
I cannot recommend reading this guide enough... It has some great advice on using Nvidia graphic cards.
That way it might still download it but it won't install unless you tell it to.. Thus letting you install the one you downloaded from the nVidia site.. 
