I have a HD2600PRO card and tried to use radeonhd as driver (which, BTW, works much better than fglrx which hangs the whole machine! :)

However, my monitor is attached by BNC cable, so there's no DDC possible. I always had to specify its parameters manually. Anyway, as there's no EDID info, radeonhd comes up with a default resolution of 1280x1024, even if there's a monitor section with HorizSync+VertRefresh for the connector in use.

After some hours of research, I found a hint that one can define a 'PreferredMode' with RandR and added

  Option "PreferredMode" "1600x1200"

to my Monitor section. At the next X restart, the server uses --after a bunch of messages-- 100% CPU and can be terminated only with SIGKILL. With ltrace, I can see that it does an endless loop of

  strcmp("1600x1200", "1600x1200") = 0

Though I haven't looked at the sources, I suspect there's something wrong with some kind of loop here :) I hope these hints are enough to find the culprit, but I could reconfigure again and supply a -verbose 99 log if you like.

This happens if there is any kind of 'PreferredMode'-Option that mentions an existing mode. Non-existing ones have no effect at all.

BTW, my current workaround is to specify a 'Virtual' in the Screen section to enlarge the possible max. resolution, and to call xrandr -s 1600x1200 from a gdm init script. This works so far, but causes additional flicker before the gdm login screen appears, and the fonts used by gdm are way too large ;)