small ati driver problem redhat 9

Installed ati drivers fom website for my ati based Hercules 9000pro.They failed at first after running fglrxconfig but fixed that by removing the autodetected vendor string from XF86config-4.
I have a "stepping" effect using opengl full screen on anything other than desktop resolution and 800x600. I can ctrl,alt+ correctly in 2d graphics.
This can be annoying as lots of games default to 640x480 and come up garbled and you have to edit the rc files.
Otherwise the drivers are as fast as in windows. ut2003 runs great.
Can anyone help?

Just to say Ive fixed it.
The culprit is horizontal monitor refresh.
You have to find a monitor config that works.
Redhat auto detects my monitor as a ctx pl7 which is correct, but to work I needed to select generic 1024 @75Hz which lowers the H sync.