The configuration file is XF86Config-4. Your old one should be backed up. Open a terminal, "su" to become root and try:

cp /etc/X11/XF86Config-4.kxconfig.backup /etc/X11/XF86Config-4

That will overwrite the new configuration file with your old one. You can now try starting KDE with the command "startx" or "startkde". You can try running kcontrol again and selecting "generic" drivers and select the driver "i810" and see if that works. It may take some trial and error to see if it works.

Another option is to boot up with the Knoppix CD using a cheat code for resolution (like screen=1280x1024). If that works, you can copy the Knoppix generated file is /etc/X11/XF86Config-4 to your hard drive and overwrite the current XF86Config-4 file on your hard drive with it.