if you have trouble upgrading from a different version of Vista, try this trick:
Start > Run: regedit.exe
Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion
Change the key : ProductName from "Windows Vista Home Premium” to “Windows Vista Home Basic”
Change the key: EditionID from "HomePremium" to “HomeBasic”
Do not restart.
Retry the upgrade.
Alternatively, you can try going directly to Windows 7 Professional from Vista Home Premium by changing the ProductName to "Windows Vista Business" and the EditionID to "Business".
Here is a chart to see what versions can be upgraded to which ones:
Worked for me just yesterday going from a beta version of Ultimate to a release version of 7 Pro.
Of course, a clean install is always better, but its worth a try.
Win 7 does an exceptional job of finding drivers, but to be sure, run this and burn the driver files to CD or USB stick or something to be sure you have 'em:
http://www.innovative-sol.com/drivermax/