Thinkpad t21 hard lockup when left overnight

[Shaya Potter <spotter@cs.columbia.edu>]

When I've left my thinkpad on overnight (without apm --suspend'ing it)
when I wake up in the morning, it's locked up hard.  For some reason it
seems to run for a few hours w/o any interaction on the machine itself,
then it just dies.  I did a test where I ssh'd into the box and ran a
simple while [ 1 ] { data ; sleep 30 } test, and it died after 3,4 hours
of inactivity.  

I've seen this at least since 2.4.13-AC5, and see it currently in
.15-pre8.  

I'm using the pcmcia package (instead of the kernel's because I can't
get my orinoco card to work with the kernel's driver) and I always have
my xircom (ibm rebranded) card inside when it crashes (so the associated
module installed). I'm also using the thinkpad module (tpctl related). 
I also have the cs46xx module installed, as well as using devfs + ext3
(though would the last 2 really have anything to do with it?).  The
kernel is compiled with usb support, and the rest should be a fairly
normal kernel build.  How would I go about trying to diagnose why the
machine is locking up hard.  

Nothing is in syslog when I reboot.

thanks,

shaya potter