On the last Free Linux Help Line show both I and another caller had an issue with getting an older model ATI card (ATI Technologies Inc Radeon RV250 [Mobility FireGL 9000] in my case) to work with recent releases of the distros we like to use. I was able to find someone who was able to point me in the right direction to get it working though. Basically you have to set:
Option "AGPMode" "1"
in the Device section of your xorg.conf. Once you have that then you can safely set the driver to be “ati”. I have tested this on both Debian Lenny and Ubuntu 8.04.2 LTS. Note that this will really only work after the you get Linux installed on the system. In my case I used the alternate CD for Ubuntu to get it going.
More information can be found on the following pages: