Sound card/speaker help

When I got my computer, I bought a really cheap pair of speakers to just get me by. Well, today I blew them with the exhaust note from a GTO. Oops. Anyway, I decided it was time to get new speakers. So after some looking I decided this would be a good idea: http://www.alteclansing.com/product_...?pID=251&sID=1

The only problem is that I am not sure if my onboard sound card supports 5.1 channels. It is an Nvidia Nforce, and on the control panel it gives me the option to switch to 6 speakers. But on the back of my comp, I only have the same dinky single plug that my old speakers plugged into. Anyone out there with 6 speakers know if there is any elaborate connection system to the back of your comp? Or is it still just the single plug? Also anyone know about compatablility issues with the Nvidia Nforce?

Thanks in advance.