Hmm... so are these crashes like with wobbly windows and openoffice (non-OpenGL applications) or with OpenGL applications (glxgears or google earth, etc). If it's the first, then I need to look into it further (how much video RAM do you have? It might be that the number of OpenGL arrays that fglrx can draw is not really fixed as <4000 but depends on your specific machine, so for me <4000 works great, but maybe for you it has to be <3000 or something). If it is only with OpenGL apps, then it is a different bug that I don't think is related. Anyway, waiting for your reply.
Also the next thing you could do is to start a regular X session, then
Then open another terminal or a tab in a new terminal (XGl is running but so is your regular X session, so you can use Alt-TAB to switch back and forth between Xgl and the regular X server apps, only trick is that when you switch back to Xgl with Alt-TAB it still thinks you are holding down the Alt key so you need to hit it before you type anything else, otherwise it will act as if the Alt key is pressed). Run emerald & beryl like this:
run :1 -fullscreen -ac -accel glx:pbuffer -accel xv:pbuffer
Now run some other apps in the Xgl session, for example:
Do some stuff until it crashes. Then you can go back to the terminal/tab where gdb is running and type:
and that will give you a backtrace. Of course it would be more helpful with a version of Xgl compiled with debugging support, which unfortunately is about 10 times as big, but it might be helpful (specifically if the lines aren't __R200TCLDrawArrays than chances are you are having a different bug).