GTA 3 is believe it or not, a pretty crappy game. I've a friend with a 2Ghz system, and a Radeon video card, and it runs kinda slow and the graphics are pretty crappy as well.
Game play isnt that good either. Of course the slowness and the crappy graphics could be a by-product of running it under Windows XP. I've not heard from anyone whos tried running it under Windows 98/ME, but I would assume although they might fair better with video, the game would still be quite choppy.
Seems like they wrote this thing for a supercomputer or something. I know many people who are greatly displeased with GTA 3.
On a side note, GTA2 (also a piece of crap).. but GTA the original is still a fun little game, even though the graphics might be somewhat elementary, its still a fun little game (I just run around killing all the cops.. ahh)