If your webcam is already supported by Linux, access it with motv. Find a summary of the supported USB devices at http://www.linux-usb.org. If you have already used motv to access the TV card prior to accessing the webcam, the bttv driver is loaded. The webcam driver is loaded automatically when your webcam is connected to the USB. Start motv at the command line with the parameter -c /dev/video1 to access the webcam. Access the TV card with motv -c /dev/video0.
When connecting the webcam to the USB before the bttv driver has been automatically loaded (for example by starting a TV application), /dev/video0 is reserved for the webcam. In this case, if you start motv with the -c /dev/video1 parameter to access the TV card, you might get an error message, because the bttv driver was not automatically loaded. Solve this problem by loading the driver separately with modprobe bttv as the user root. Acess an overview of the configurable video devices on your system with motv -hwscan.