There is indeed a Linux driver for the video-in on the [789][56]00, called "planb", but it has several unresolved issues (notably, from what I understand, no V4L2 support) and was recently dropped from the kernel due to neglect (2.6.26 is the last version to include it).

I used it in the past on my old 7600, and it worked well for what it was, but had a nasty tendency to lock up at times.

-lee