How to check your PC is Windows-Vista compatible
 

Microsoft has a tool for people to see if your Windows XP-based PC can run Windows Vista: the Windows Vista Upgrade Advisor RC.

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.

Note: This software isn’t final, so the results you get may not be 100% accurate. Make sure you run Upgrade Advisor again in a few months for a more accurate assessment and to get the latest up-to-date information about whether your system is ready for an upgrade.

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.

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Source: Microsoft.com