This may not answer your specific question, but if you haven't used this tool, you should give it a try.http://www.microsoft.com/windowsvista/getr...or/default.mspx
Windows Vista Upgrade Advisor
Want to see if your Windows XP-based PC can run Windows Vista? Just download, install, and run the Windows Vista Upgrade Advisor.
This small software tool will scan your computer and create an easy-to-understand report of all known system, device, and program compatibility issues, and recommend ways to resolve them. Upgrade Advisor can also help you choose the edition of Windows Vista that best fits the way you want to use your computer.
Before you begin
Before you run the Upgrade Advisor, be sure to plug in any USB or other attachable peripheral devices (such as printers, external hard drives, or scanners) that are regularly used with the PC that you're evaluating.
Download Windows Vista Upgrade Advisor
The Windows Vista Upgrade Advisor works with 32-bit versions of Windows XP and Windows Vista. It will not work with Windows 98, Windows 2000, or Windows XP Professional x64 Edition.
Here are answers to some common questions about the Windows Vista Upgrade Advisor.
The Windows Vista Upgrade Advisor does not collect or send any personal, identifiable data to Microsoft Corporation or third parties. See the Upgrade Advisor privacy statement for details.