I recently made my own surround sound system using 3 old sets of speakers. Wired them to run from the one plug, put the audio controls and a master switch into a new box, and there ya go, surround sound for a tenner
Still missing a decent sub-woofer for bass notes, using a huge fugly speaker hiding under the bed at the moment. Works, but it's just not right
The computer (assuming you're not using the most basic of on-boards sound) should have 3 ports out (that you need anyway). One for surround, one for center, and one for front. I put 2 speakers into a couple of nooks and crannies behind my chair (pics tomorrow, also building the new pc!), and they're surround. 2 sit either side of my chair, for front. And one small one sits behind the monitor for center. It's not the most ideal of setups, but it functions as surround sound, and I can't afford a decent alternative at the moment