Anderton
I recommend installing a PCI card with USB ports for audio...
+1000
I've done this (first PCI, now PCIe) for every USB and Firewire interface I've owned in the past 8 years and, not so surprisingly (to me anyway), the result is smooth sailing with interface performance.
Sure, you can try your luck with one of the onboard USB/FW ports, but this just as often results in incompatibility or resource-sharing issues. Installing a dedicated PCI(e) card gets around all of that.
Of course, this only works with a desktop. With a laptop, you're stuck with what's there.