You can upgrade, just not to a PCI soundcard. You must use PCMCIA, Firewire, or USB.
The US-122 doesn't have the greatest sound quality, but it is adequate, and has preamps with phantom power. I wouldn't recommend it for a desktop where you can use better-quality PCI cards for less money, but it's more of a tossup with a laptop. If you get one, you should be able to find one for about US$200 - don't spend much more than that.
post edited by sinc - 2006/02/15 08:03:10