Need a 5.1 capable Receiver to put the surround sound signal out to all accessories (Xbox, TV, PC, etc), as well as all 6 speakers (center, front left/right, surround left/right, and sub-woofer)
TV has to have BOTH input and output to be able to get the sound back to the receiver. TV's that have only the "standard" plugs, are input plugs only (for game systems, camcorders, etc).
I have a PS2, my desktop PC, TV, and DVD player all hooked into my Kenwood 5.1 Receiver, and they all get a digital surround sound.
Ah, and your PC needs to have a 5.1 sound card to be able to actually play in surround sound
It would help to know what type/model receiver (or stereo) that you have, to be able to know if you can get surround sound at all!