Recent versions of the Linux kernel include a generic video capture API, Video4Linux. You can find out more about it, including how to subscribe to the new mailing list, at the home page.
This is the source to a simple frame grabber I bashed together to collect frames from my QuickCam for putting on the web. It spews out a PPM file, which is easily converted to a GIF or whatever with a bit of shell plumbing. Who knows, someone might find it useful.