I'm kind of shocked that his sound card doesn't has support under ALSA or OSS - What's the chipset? Is NetBSD an option if Linux isn't?
On a more on topic note, I've had good experiences with my Logitech USB headsets. 350 something or other is what they're called. Anything with the same chipset should work. Can't personally vouch for anything else, but they sound like the USB sound cards are fairly standardized: http://www.linux-usb.org/USB-guide/x319.html
That said, if this thing is as old as it sounds, you might want to check and make sure that the USB ports actually work with reasonably modern devices before spending any money. Might have to buy one of those old PCI add-on USB controllers.
-Sean Crago/MrZaius MrZaius.com