I created the attached doc but here's a quick paste of it:
Download How to remove the 90 days Windows 7 Enterprise trial period deployment with an MSDN license key for Windows 7 Enterprise.
Download the free 64bit trial version from here:
Link Removed (CTRL+Click to access the link)
Or copy and paste to a browser:
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Locate your My Computer icon and right click select to choose Properties to go to this screen.
This is the default screen you see for My Computer Properties. You'll see that on the desktop background bottom right corner (yellow circle), it shows, "Windows 7, Windows License valid for 90 days, Build7600." You also see the "Change product key" option shown in blue circle. Also note (to compare to after unlocking the trial) that the yellow underline shows, "Your Windows license is valid for 90 days."
Select the "Change product key" option.
Punch in your MSDN key.
Note:
Windows will require an active Internet connection in order to activate the new key. If you do not have an Internet connection, the following screen will appear giving you other options shown below.
Once the MSDN key is verified, Windows will be activated as shown below:
Notice the desktop background does not warn of the Windows license 90 days trial period. It also now shows in the My Computer properties that Windows is now activated (without the 90 days trial limitations).
The user perspective for activating is to be able to continue using Windows with future update and security patches for stability. So Windows Update is tested after the new key activation to ensure functionality is not broken.