Get the 32-bit upgrade version of Windows 7 and run the setup program off the DVD from within Vista.
If you want to go to 64-bit Windows 7, you can still get the upgrade version but you won't be able to do an inplace upgrade. You'll have to backup your profile data using Easy Windows Transfer and then do a clean install of Windows 7 64-bit, restore your profile data and reinstall all your apps.
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: http://windows.microsoft.com/en-US/windows7/help/upgrad...
Please refer to Microsoft official site for Windows 7 Compatibility with your hardware and software (There you will find out about hardware and software compatibilty.) http://www.microsoft.com/windows/compatibility/en-us/de...
There is a pulldown from which you can choose "hardware" and "software".
At this point you can run the Windows 7 upgrade DVD. Depending on your hardware it can take up to several hours.
Let me know if this helps!
Windows 7 Client Team Support