Mike,
What's your budget? How big is your room?
Will you be playing ripped CDs, internet streaming, and/or DVD movies through the computer?
Will you be using the computer monitor or a TV?
It's hard to beat the little AV-123 xls 2-way standmount speakers for $110 each.
Picking a sub is up to how big the room is, how deep you want to go, and how loud you want to get.
I don't know much about computers, but a Panasonic SA-XR55S 7.1 receiver for $200 (street price) looks good.