Frequently, when I run Xconfigurator --preferxf4, it freezes the machine solid while trying to scan for monitor parameters. It doesn't seem to matter whether I have X running on another console or not. It has never done this the first time I've run it after boot.
What card type?
My video accelerator is a Matrox mgag200 AGP, 8mb
I got it to crash again, this time with a strace. It seems to go into an infinite loop calling vm86 and recieving 'function not implemented' from the kernel. after a few seconds of this scrolling by, the system locks with no sysrq, as mentioned before.
some combinations of hardware do not like to be DDC probed. This will probably not get fixed (You can choose not to probe) until a rewrite of Xconfigurator takes place.