For the graphics card, this is a good one:
BFG Tech BFGR6600GTOC Geforce 6600GT 128MB 128-bit GDDR3 AGP 4X/8X Video Card - Retail
RAM, get two new sticks and put it in dual channel mode. Use the spare RAM you have now for testing or spare parts:
CORSAIR XMS 1GB (2 x 512MB) 184-Pin DDR SDRAM Unbuffered DDR 400 (PC 3200) Dual Channel Kit System Memory - Retail
You'll have a pretty darn good system with those. I was thinking of giving you some DDR500 RAMs but I don't know if you can OC your BIOS to do that. The DDR400 for this one is pretty good with low latency.