I'm running this Windows Vista on

Acer Aspire 1692WLmi ( 1.73GHZ, 533FSB, 2MB L2 Cache)
15.14' WXGA Cyrstalbright TFT LCD
ATI Mobility Radeon X700 PCi Express 128MB VRAM
80GB HD,
Slot Loading DVD-+RW
2GB DDR 2 Dual Channel

I found the 2GB is just nice to run the Operating System but sometimes is still slow since the OS take lot's of RAM running it now using best performance mode and no lagging or problem, if you're on 512MB RAM don't dream to install Vista Ultimate to ur PC or Laptop,i'm sure it will be very slow.

DX9 card are:-

Nvidia 6 series and above
As for ATI, I believe its for 9500 and above...

If you want SM3, yeah, then its X series and above...
Honestly nothing to shout about Vista... Im downloading the RTM via some torrent and already have a crack for the expiry date. Im not sure which version Im using via the screenshot cos I borrow the dvd from my bro. In true, Vista is bloated. Apple does the same if not better effect for Aero alike theme and they did it with 512MB or less. M$ is basically screwed. There's no reason to install vista now cos there are not enough drivers for it. If you want to try it out, dual boot. You will regret if you format your windows xp partition just to install vista.