Microsoft has updated its Get Ready website to include the minimum system requirements for Windows Vista. As Nick White pointed out in the Windows Vista Team blog, you need a minimum of 800 MHZ, 512 MB RAM, a DirectX9 graphics card, and etc. You can view more information at the Windows Vista Get Ready website.

Windows Vista Capable and Premium Ready PCs
http://www.microsoft.com/windowsvist...y/capable.mspx