I don't think you're understanding how these things work. It may be because of the use of "card" which is that holdover from when all sound cards were expansion cards we put into computers. If you're talking about a
USB sound card, it'll simply work as a device that you plug into the computer to your USB port. They're
peripheral (external) devices like the ones mentioned in the stickies of this forum. Drivers may be needed, but often aren't so long as your computer is USB compatible. I think USB 1.1 is sufficient for streaming audio.
The other kind of sound device/card is an expansion slot sound card. These could be old ISA-based sound cards (like my first), PCI-slot soundcards (which I currently use), newer PCI-e sound cards, or even some that are built right into the motherboard itself. They're not USB cards, nor do they plug into USB ports.
Those CMedia sound cards are usually USB external soundcards, good for laptops or systems that you don't want to mess with opening the case. CMedia might also have some internal, PCI cards, but I haven't gotten any of those, and they're probably not so convenient for a DAC. Remember to always look for "USB" in the sound card title if you need one that is not an expansion slot card.
As for drivers, many USB sound cards work straight out of the box as an USB streaming device because of the USB standard. I don't know if WinXP is equipped for that; however Win7 it came with drivers that worked with my USB card out of the box. You should just plug the USB soundcard into your Dell and see if Windows XP accepts and uses the CMedia card as a 7.1 device, and if not, then find some drivers to use with it.
Oh yeah, and if you need an external CMedia card,
here is the one I got working (Amazon.com). It needs USB 2.0. Make sure your Dell supports that.