All you need is a simple 1/8" to RCA adapter. This works extremely well. The adapter is all streight hardwired (by that I mean no wires, solid metal with plastic surrounding it, so it's all very solid and conducts very well). Pick it up at any radio shack.
If you want an amazing card get the Creative labs X-FI elite pro. I bet you could find it online for $250 or less. It uses professional DACs, You'll be blown away by the sound. And dont worry these cards are made to deal with whatever goes on in the PC and be able to put out amazing sound. You can check out my system to see what I did. I actually think this is a more purist and simpler way of doing things and prefer it all on my PC for my front end. I also recommend the firefly remote and the software that comes with it.