*tip* - you'll get more/better responses if you do some research on what's out there and give a proposed build of some sort... then ask for advice on that. "what should i get" is too general.

that said... this is my current setup:
-core 2 quad q9550 (running stock @ 2.83 atm, had it oc'd to 3.5 at one point before i changed out some hardware... working on it again this week)
-4gb ddr2 800 (upgrading to 8gb when i install 64-bit vista this week)
-bfg gtx 280 OC2
-2x 500GB HDD's in raid 1

i run 4x slaves on second monitor @ 800x600, medium graphics; 1x main @ 1680x1050, high graphics
runs pretty smooth except when all my guys are in a big city, mainly because my memory is being maxed out i believe... so vista 64 and 8 gb memory should help with that.