Just an FYI, when upgrading from Windows Vista to Windows 7 you must upgrade the version currently installed within Windows Vista to the corresponding version in Windows 7. I.E. Windows Vista Home Premium to Windows 7 Home Premium; Windows Vista Business to Windows 7 Professional; and Windows Vista Ultimate to Windows 7 Ultimate. You also cannot upgrade a 32-bit operating system to 64-bit -- to migrate from 32-bit to 64-bit will require a custom install.
Please check out the requirements here for Windows 7:
If you want to run Windows 7 on your PC, here's what it requires:
•1 gigahertz (GHz) or faster 32-bit (x86) or 64-bit (x64) processor
•1 gigabyte (GB) RAM (32-bit) or 2 GB RAM (64-bit)
•16 GB available hard disk space (32-bit) or 20 GB (64-bit)
•DirectX 9 graphics device with WDDM 1.0 or higher driver
You can find the official Microsoft Windows Upgrade Advisor here: Windows 7 Upgrade Advisor
Before making any attempts at upgrading your Windows operating sytem; you should first backup all of your important data!
You can also go with the easy transfer, there is a very well planned out tutorial on the microsoft site: Upgrading from Windows XP to Windows 7 - Help & How-to - Microsoft Windows
Also, please refer to Microsoft official site:
Windows 7 Compatibility: (There you will find out about hardware and software compatibilty.) Windows Compatibility Center
There is a pulldown from which you can choose "hardware" and "software".
Finally, if you want to do some research; there are also some great articles, instructional videos and such to help with your Windows 7 migration and upgrade decisions located at our Springboard site: Windows Client | Deploy, Manage, Desktop, 7, Vista, XP | TechNet
Thanks again and good luck!
Microsoft Windows Client Support