It was a fruitless 3-day battle: I could not get the ATI RV370 (Radeon X300) on my desktop Dell to work with Xorg. I tried the pre-packaged fglrx driver, I tried rebuilding it with modules-assistant, I tried installing the latest version from ATI's support site.
The kernel module would load fine but X would core dump after initialising the driver, DRI could not be enabled or X would freeze whenever any OpenGL application was run. I went through heaps of support forums and saw many users having similar problems.
In the end I got myself a nVidia 7300LE and, let me tell you, it was the best $AU70 I have ever spent. I simply wanted to be able to watch DVB-T on my computer, so this low-end card was more than enough.
The installation was effortless and it worked on the first try, even with "Composite" enabled; it's true that it didn't update the device description on xorg.conf but I did that manually just to be neat.
I should have given up on ATI years ago after my all-in-wonder died on me shortly after a year.