Ah, now that I read it again I see what you meant, just misinterpreted it. Anyway, depending on your sound card, I'd suggest you get a small plate amp and put that sub in a box. I'm not sure if any subs come with those mini jacks that will plug in your sound card, you may need to cut some cables and stuff and make your own adapter somehow.
The other option is to find a crappy receiver (maybe just an old one laying around) and connect the sub to that with the PC sound out going into the receiver. No matter what you do, it's probably going to cost you a little bit of money and it's definitely going to be rigged >_>