Microsoft finally announcing to public about minimum hardware specification to run Windows Vista. Windows Vista operation still remain require 1Gb Ram.
Minimum Requirements (Vista-Ready PCs):

• 800Mhz Processor
• 512 MB of RAM
• DirectX 9-Capable Graphics Processor

Recommended Requirements (Premium-Ready PCs):

• 1 Ghz Processor
• 1 GB RAM
• 128 MB Graphics Memory (along with many other graphic requirements)

Microsoft announce this hardware specification because of WinHEC (Windows Hardware Engineering Conference). So, The attendance of WinHec will get a copy of Windows Vista and test run it.

News Source:- Microsoft Watch