Windows Vista - http://www.vistaarticles.com
Windows Vista Requirements
http://www.vistaarticles.com/articles/51/1/Windows-Vista-Requirements
By 
Published on 05/19/2006
 
Today, Microsoft Corp. announced the launch of the Windows Vista “Get Ready” Web site, the worldwide availability of Windows Vista Capable PCs, the upcoming availability of Premium Ready PCs and the availability of the Windows Vista Upgrade Advisor beta.
Windows Vista Requirements

Windows Vista Capable

Modern processor (at least 800 MHz)1
RAM 512 MB
DirectX® 9 capable
(Windows Display Driver Model (WDDM) support recommended)

Windows Vista Premium Ready

1 GHz 32-bit (x86) or 64-bit (x64)1
RAM 1 GB
GPU Runs Windows Aero2
Graphics Memory 128 MB
HDD 40 GB
HDD Free Space 15 GB
DVD-ROM drive3
Audio output capability
Internet access capability

Windows Aero requires the following:

* DirectX 9-class graphics processor that supports the following:
* WDDM
* Pixel Shader 2.0 in hardware
* 32 bits per pixel
* Adequate graphics memory
* 64 MB of graphics memory to support a single monitor less than 1,310,720 pixels
* 128 MB of graphics memory to support a single monitor at resolutions from 1,310,720 to 2,304,000 pixels
* 256 MB of graphics memory to support a single monitor at resolutions higher than 2,304,000 pixels
* Meets graphics memory bandwidth requirements, as assessed by Windows Vista Upgrade Advisor running on Windows XP

Details:

http://www.microsoft.com/presspass/press/2006/may06/05-18GetReadyPR.mspx