On Tue, 2005-10-25 at 15:37 -0500, Miles O'Neal wrote:
..
> There's nothing suspicious in the logs;
> they just lock up.  Both systems that
> locked up today had the CAPS LOCK and
> SCROLL LOCK keyboard LEDs flashing.

This usually indicates a kernel panic (good sign, since the kernel will
try to tell you why it fell over). You can either

*  get somebody who knows Morse to read these flashing LEDs. No, this is
not a joke, check /usr/src/linux-*/kernel/panic.c

* try to hook the machines to a "real" console without powersave or a
serial console. Even if the message didn't make it into the log, there
may be something on the console.

And lastly, perhaps you should try with the most recent kernel
(2.4.21-37) available before discovering "old" bugs.

HTH
Jan