Though not all that familiar with Linux, to my knowledge they have not yet gotten to AGP cards. Check out the Linux forum also available on the My Desktop Network. (That little icon in the upper left.)
With the most recent release of XFree86 (the
X Window System for Linux) a few AGP-based
video cards are supported. (I am looking to
upgrade my CPU, MB, RAM, video card, and
monitor in December, so I've been hunting around for information on this, too.) One place to find this information is at "http://www.XFree86.org" (without quotes, of course). You'll need to scroll down a little to look at the FAQ (click on the link), which has some information on which AGP cards XFree86 3.3.2 supports. Also, Red Hat Linux 5.1/5.2 support some AGP cards under XFree86; Red Hat's address is "http://www.redhat.com". Click on "Red Hat Linux 5.2", then scroll down a bit so you see the word "hardware" underlined; click on it. This is the RH Linux 5.2 Compatibility list (which is probably not a whole lot different from 5.1's).