well as you may have gatherd from the other replys, there realy is no way to have a USB webcam on your robot... and besides its not allowd.
HOWEVER, if you wanted to use an imaging device to, say, find stacks, Parallax offers a product called the "CMUcam" which:
communicates using a TTL level serial port and has the following functionality:
>Track user defined color blobs at 17 frames per second, find the centroid of the blob
>Gather mean color and variance data
>Arbitrary image windowing
>80x143 resolution
>9600 baud serial communication
>Automatically detect a color and drive a servo to track an object
>Slave parallel image processing mode off a single camera bus - advance function
>Ability to control 1 servo or have 1 digital I/O pin - advanced function
>Adjust the camera's image properties - advanced function.
(
http://www.parallax.com/detail.asp?product_id=30051)
Well anyway, its not what your looking for but it is prety cool anyway, -Jacob