For agpgart add the line:
options agpgart agp_try_unsupported=1
in your /etc/modules.conf
I started getting the X freeze when I updated my LM9.0 kernel to 2.4.19-35 from 2.4.19-32 (and increased RAM to 768MB).
Reducing by BIOS AGP multiplier reduced its frequency, but did not fix it. I still don't have the solution.
I've found I can get out of a freeze by using
Alt-PrintScreen-k (see /usr/src/linux/Documentation/sysrq.txt)