Hi,
Taken from VISTA web site MS establishes that a VISTA capable machine
requires minimum of 512MB of RAM but to have premium capablity (e.g. Aero)
should have 1GB RAM.
"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.
Windows Vista Premium Ready PCs
To get an even better Windows Vista experience, including the Windows Aero
user experience, ask for a Windows Vista Capable PC that is designated
Premium Ready, or choose a PC that meets or exceeds the Premium Ready
requirements described below. Features available in specific premium editions
of Windows Vista, such as the ability to watch and record live TV, may
require additional hardware.
A Windows Vista Premium Ready PC includes at least:
1 GHz 32-bit (x86) or 64-bit (x64) processor1.
1 GB of system memory.
Support for DirectX 9 graphics with a WDDM driver, 128 MB of graphics memory
(minimum)2, Pixel Shader 2.0 and 32 bits per pixel.
40 GB of hard drive capacity with 15 GB free space.
DVD-ROM Drive3.
Audio output capability.
Internet access capability."