Well in my case I've got two computers here running Vista Ultimate.
In the case of the former it won't run my fave "Really Slick
Screensavers" (
www.reallyslick.com).
The former has no graphics card. The onboard video (ATI Radeon Express
200 w/shared 128 MB RAM) runs Vista Aero *very* nicely, but as soon as
I tried to launch the above mentined (3-D intensive) screensavers
things got rather ugly.
So *without* a video card this box is excellent for 2-D (+ all Vista
bells and whistles) but any 3-D apps are out of the question.
Since the primary user of this box rarely does anything beyond
websufing, e-mail, word processing and light photo editing, it's not
an issue.
The other box (my primary one) has a 256 MB NVIDIA GeForce 6800 GT
video card and runs the previously mentioned screensavers very well.
I'm not into games, so I can't speak for their performance.