Kernel panic while running X - how to diagnose?

[Chris G]

I'm getting very occasional kernel panics on my xubuntu 8.10 system.
By "very occasional" I mean maybe once a week or even less but they
tend to come in batches, for example it's happened three or four times
in the past few days after not having happened for a week or two.

It doesn't seem to be happening when running any particular
application though it *feels* like it happens when graphics/display
work is happening.  E.g. it has happened sometimes when Firefox is
updating the display.  I don't think it has ever happened when I'm not
using the system, it runs 24 hours a day as it also acts as a server
on our home LAN.

The symptoms are a total freeze of the X desktop and usually the
keyboard lights start flashing which I believe is indicating a kernel
panic. 

There's nothing that I can see in any of the log files in /var/log. 
Before all the logging that occurs when the system is restarted there
is only the normal "things happening" logging, nothing at all out of
the ordinary.

The motherboard is an Asus P5Q-VM, Intel chipset.  The temperatures
are ridiculously low (32 and 20 Celsius) so I don't think that's the
issue. 

What can I do to diagnose the problem?

-- 
Chris Green