In some cases your media player (VLC, mplayer, amongst others) will need to know the video and audio device files for your webcam.
It uses the gstreamer library, which utlilizes the video4linux2 API.
This is a list of software that allows you to do a simple 'plug-in-and-go' test with your webcam.
This means that you should be able to plug-in your webcam and use it straight away: no driver disks or installation.
To test whether or not your webcam works in this way, install Cheese, a GNOME program for capturing video and stills from a webcam. Cheese is included in the Main repositories since Ubuntu 8.04 LTS (Hardy Heron).