I run it under XP Pro without problems. You need to update XP with a patch. The info on this is available on GTA3's website.
I don't have a "supercomputer", but, I do have an Asus P4T-E with i850 chipset, 1gig RIMM and the Asus 8460 Ultra 128mb graphics card. The Audigy Platinum and Inspire 5.1 digital 5700 series speakers don't hurt either.
No slow or crappy graphics. Check the patch, I DID have a problem at first, but, after installing the patch, no probs.