First, make sure you have the webcam drivers in a directory on your pc, the driver can be d/l with the FRM tools here...
Sunplus FRM Tools with driver
Make sure your pmp is turned off when plugging in the USB. On my spmp3052 based unit it was the ESC button that did the trick, keep trying buttons until you get it.
When you hear the new usb device found point it to the directory with the drivers.