The minimum recommended or the minimum that I've seen work before?
I've heard of stories of 256MB of RAM working with Vista with some features
disable of course. I've heard of people getting it to work with later
Pentium IIIs. I've even heard of people getting Aero Glass to work on PCI
video cards. (Yes, PCI, not PCI-Express.)
Now, as the minimum that Microsoft recommends:
512MB of RAM
A 'modern' processor. (Define modern and you'd have it made, but
unfortunately they don't. My guess would be Athlon XP's (Semprons) on up or
Pentium 4's or Celeron D's on up.)
Vista I believe eats 8GB of hard disk space, and you need a minimum of a
20GB partition I think.
You'll find it very, very beneficial to have at minimum a DVD drive. (Yes,
DVD, not CD.)
Any video card that works on XP should work on Vista, but to get Aero Glass,
you must have a direct-X 9 card that supports Pixel Shader 2. It must also
have a bare minimum of 64MB of video RAM to get Aero Glass, but 128MB is
recommended, and 256MB is ideal. An NVIDIA Geforce FX5200 (FX5100 for
notebooks) on up or an Ati Radeon 9500 on up are the minimum GPUs for Aero
Glass. AGP 8x or PCI-Express 16x is recommended, but I believe AGP 4x works
also. Keep in mind, that an FX5200 or Radeon 9500 will probably only run
smooth at lower screen resolutions such as 1024x768. You might be pushing
your luck a little bit by expecting an FX5200 to work smoothly at 1280x1024.
(Not saying that it won't.) (As I said, I've also heard people getting
Glass to work on a PCI video card if they have a supported GPU. For
example, an NVIDIA Geforce FX5500 PCI video card, but I doubt the
performance was ideal due to the limited bandwidth of PCI.)
Now remember, Microsoft hasn't released official requirements yet, these are
just as of right now what they recommend as guidelines. They may change for
the better or for the worse. I've heard they might have the official
requirements ready by some time this summer. (Somewhere around June or so,
but don't expect it.)