The ati fglrx driver is still not working for my Radeon HD 4200.
I am sure I can get it working as I did before using alternative drivers, but preffer to test and report bugs to try to help get the official driver working.

Without any driver the card works great in kubuntu 10.04 with the exception of 3d rendering being slow. All of the composite effect work great.
Unfortunately after I install the driver the desktop will not load even after I un-install the driver.

The simple fix seems to be to just delete /etc/X11/xorg.conf or copy the failsafe xorg.conf file, after doing either and re-booting the desktop the desktop loads but will not do composite rendering.

If I do a full restore from a .tar backup I have the same problem.

The fix for this is to delete the following directories:
/usr/lib32/fglrx
/usr/lib/fglrx
/etc/ati

Then restore the backup and everything is back to normal.

I imagine simply un-installing the fglrx driver and deleting those directories would fix the problem as well.

I will try that first next time and post back here.

If you do not have backups of your system I highly recommend creating tar backups. See: http://regx.dgswa.com/html/node/29