Hooking up Surround Sound

[DemoniC]

Hello, I have a Dell E310 Dimension which I got for christmas 2005. I have always had the cheap old speakers that come with new computers and wanted to upgrade. My sister got computer from her grandpa when he passed away and it had a 5 speaker w/woofer set up. She chose to swap out with me since she didnt have a need for so many speakers. The surround sound is Dell/THX but I have no idea the model. It has a built in wire with three connectors to hook up to PC. My PC has 3 ports in which one is for mic, line out, and line in which is standard i believe. The colors for the ports are as follows: Mic-Pink, Line Out-Green, Line In-Blue. The woofer has a green, yellow and black plug. I plugged in the green obviously for the sound but have no idea on how to get the back and center speakers to work, all i hear is sounds like its on. I was just curious to if there is a way I can hook it up with my general sound card that came with my computer or if I need to purchase a new sound card and which one I should purchase to fully hook up the system....ie the correct ports for the plugs. It doesnt have to be expensive, actually i would rather it be cheap as possible. Thank You