Gta3 before the pach could barly run on any computer, True my computer had a problem with GTA3 at the start, but now my secondary computer with a GF2 can do it fine.
If you want to go AMD I suggest.
2100+ or 1700+ either will give you 2Ghz but the 2100+ will push 2.5 with a little higher end cooling. IMO with that I would get the SLK-700 or a little better the SLK-800
MotherBoard, The KT400 chipset is not much better than the KT333 but If you must have newer then be ready to pay an extra $15 per MoBo.
Ram At leats 512mb for Games. PC3200 if you can afford it.
Video If you are into mods you can get an 9500 and transform it into a 9700 by placing a resistor to a different place, and thay are much cheaper than the 9700.
Harddrive try to get an 80GB, if you can afford it then grab the 8mb cache ones.
That is the basics all the extras you can debate over.