So if I'm understanding you correctly, when you don't have the card plugged in, your system boots normally, but when you do, it doesn't even make to the boot screen? Maybe you should check whether the card is correctly inserted into the slot. This sounds closer to a hardware error, not driver error. Maybe you can try a different slot as well?
I tried once to put a GeForce 9400 (PCI) in a U10 and it didn't work -- it also didn't work in a Pentium III. There seems to be some minimum PCI spec / power requirement in order to boot that card. The same card in a newer Intel system worked fine, and conversely, an older GeForce 440MX PCI worked in the U10 (under Linux, with full OGL!)
However, I would think that a USB card wouldn't have a very high set of requirements...