Windows Vista Hardware Requirement

A Windows Vista Capable PC includes at least:
A modern processor (at least 800MHz1).
512 MB of system memory.
A graphics processor that is DirectX 9 capable.

A Windows Vista Premium Ready PC includes at least:

1 GHz 32-bit (x86) or 64-bit (x64) processor1.
1 GB of system memory.
A graphics processor that runs Windows Aero2.
128 MB of graphics memory.
40 GB of hard drive capacity with 15 GB free space.
DVD-ROM Drive3.
Audio output capability.
Internet access capability.

Get further info on GetReady Microsoft Windows Vista