Stupid question, I think I know the answer already. If I have a sound card that doesn't support 5.1 and I have 5.1 speakers, the speakers are just going to sound like regular ones, right. because the sound card can't handle that kind of power?
Yes, you need a 5.1 soundcard to take advantage of 5.1 speakers. It's not an issue of power though; it is an issue of providing the discrete rear and center/sub signals.
Anyway, what is a good sound card that supports 5.1?
Edit: and is an affordable sound card.
IIRC all of the Creative cards from SB Live! onward will do 5.1. Turtle Beach Santa Cruz will as well.
Sound Blaster Live is cheap, it's ok. Nothing special.
What sound card do you have now? If it can't support 5.1 then there wouldn't be a place to plug the surround or center speakers in.
Unless I did something wrong, all the speakers plug into the subwoofer which plugs into the sound card.
How many cables go from the sub to the soundcard? Unless it is a digital connection, there should be 3 (front, rear, and center/sub).