dividox, I'm not a fan of spending a lot on a soundcard. The environment inside a computer doesn't strike me as being a good one for digital to analog signal processing.
Instead, for my Windows XP Box, I use an Edirol UX-1D (I think that is the number)--USB audio device with a simple coax digital out. That goes into my Theta Pro Basic IIIa DAC. Sounds as good, I think, as I've ever heard mp3s sound. B'sides, its *cheap* compared to high end sound cards, and you can always change later if you don't like it...
I've also used the M-Audio Sonica, which is a similar device but with toslink optical out. I'm not sure what Jewel Hasan was talking about with the Sonica--there is no DAC on board. Or, maybe the Sonica has changed. Mine was a little blue thing smaller than a pack of cigs with an blue LED that showed when a signal was present, a USB in on one side and a optical connector on the other. No analog conversion.
For a while, I had the Sonica hooked up at the computer, and then a 25' run of toslink to the DAC. I found some powered USB cables, and switched it so it was 25' of USB and the Sonica right next to the DAC. The difference was not subtle. If you have a long run, go with USB.
The Windows XP integration with the Edirol seems more bulletproof than the Sonica. I seem to recall that the Sonica occasionally glitched.