Morph...
All advice above is pretty solid...the real key is what you want out of the system. you can build a great AH2 system for about ~$650 including video (assuming you have ok monitor now).
ASUS/ABIT/Gigabyte all make good high quality MB's that are good if you want to overclock. If your not the OC type a bunch of "2nd tier" MB's also would work DFI Shuttle ECS MSI IWILL SOYO all have decent products (ECS is very spotty on quality but they're great if they work:)).
You can get a decent 2500-2800+XP combo a bunch of places on line or from fry's.
you'll want to get 2 x 256 2700DDR (or 3200 if you get agood deal) instead of 1 x 512 if you get a barton core AMD XP+ (2500 and above)...
I'm running a Ti 4200 MSI card...still whups on most of the "new" cards...Ti 4600 is even better.
Any case with a good power supply (350W or better) is OK...400W is better in long run. If your really just buying for AH2 then "go low" and save the coin. You'll have it if you need to upgrade for AH3

in a couple of years...