Ok. So I'm on a tight budget for my computer speakers. I would like to have a decent set under 100 dollars. I have a Sony STR AV580 reciever and three sets of old speakers: a pair of JBL Pro III speakers, a pair of Boston CR6s, and a pair of Infinitys (not important because they sound like crap). I have no sub. I would like to set up a surround sound system (4 or 5 piece) so games and movies sound better. Is my reciever and budget so bad that I should dump my current stuff and get some decent computer speakers or is there a good choice within my price range that will sound better than computer speakers. Another question: I am hooking this up to an older (P2 450mhz) Sony computer with whatever soundcard there is on it. I am currently hooking my sound card to my reciever with a Y splitter cable to get 2 channel sound. For 4 channel or 5 channel sound, would I need a new sound card or will my old one work? Thanks for the help. BTW I'm a complete newbie to audio stuff so please don't get too technical. 
