Experimental driver - they are not kidding!
I recently received a SIIG webcam ("MobileCam/Light Pro") as part of a package deal.
After plugging it into a low-speed USB port and seeing only a garbled picture, it completely locked my Kubuntu 6.06.1 LTS system. Hard. Keyboard did not work, no way to login remotely. Had to hard reset.
Beware, when the Spca5xx page says
The spca5xx driver supports a wider range of cameras, but classifies itselves as experimental. (This means it might crash your kernel in the worst case.)
they are not kidding.