I'll try to put this as simply as I can. As long as the sound card is by Creative Labs, and the sound card fits in a slot you have available on your motherboard, then it barely matters what you get. I get excellent sound from my card. My card is a PCI Creative Soundblaster Audigy SE that I got a year or two ago for $30. Driver support for it with Windows 7 gave me a little bit of trouble, but I got it to work anyway. It's an old card...what can I say? Driver issues are to be expected in such a case.
Regardless though, the general rule of thumb still stands. Just let me know how much you're willing to spend and what slot you have and I can link you to an appropriate card if you like. Cards go for anything between $30 and $300 bucks. There are PCI-Express versions and PCI versions as I'm sure you're aware.
If there's anything that needs further explanation, please ask. I'll be happy to answer.