Crystal CS4280-CM 64-bit 4-Channel PCI Sound Card - $8.95 + $5 shipping

[FPSguy]

You can get it at CompGeeks.com. You may be able to get an additional 10% off using one of the codes available elsewhere. I am not sure about the quality of this card, but it seems like a decent enough price for a new retail 4 channel PCI sound card that claims to be XP compatible. If you don't like this one, maybe the one in this thread will be more to your liking.