I have a similar problem.
When X starts it is often garbled and unusable.
Ctrl+Alt+Backspace might cause the system to freeze.
However sometimes with I flick between the tty console on Ctrl+Alt+F7 the X screen redraws correctly.
My Thinkpad T30 uses a Radeon mobility too.
I am using Ubuntu dapper, so it's not KDE specific IMO.
I have a similar problem.
When X starts it is often garbled and unusable.
Ctrl+Alt+Backspace might cause the system to freeze.
However sometimes with I flick between the tty console on Ctrl+Alt+F7 the X screen redraws correctly.
My Thinkpad T30 uses a Radeon mobility too.
I am using Ubuntu dapper, so it's not KDE specific IMO.