Microsoft has yet to unveil Vista's official requirements. The company, which has said it would not finalize them until summer, has thus far recommended that customers who wish to upgrade and take full advantage of all Vista UI features purchase a machine with a discrete graphics card that supports its DirectX 9 graphics framework, Windows Display Driver Model, 32 bpp (bits per pixel) color depth, and which contains at least 64MB of graphics RAM.
It has further hinted that Vista technologies, such its Max user interface for Windows XP, should be used on PCs with at least a 2.4GHz processor, 512MB of RAM, and a graphics card capable of handling its Windows Presentation Foundation. Such a card, the company says in an online FAQ, should be "the fastest PS 2.0 [Pixel Shader 2.0] card with the most memory your bank account can afford," such as ATI Technologies Inc.'s Radeon X800 or Nvidia Corp.'s GeForce FX 6800.
More here... Source : eWeek