> It may not be the same problem.  When I took DDB out of my kernel, the
> system did a crash, rather than a lockup.  

That suggests that the "lockup" was actually a crash into DDB; you
couldn't see the DDB prompt..

> It rebooted, and I now have a core file (actually, a netbsd.0 and a
> netbsd.0.core, in /var/crash/).

As a first step, can you get a backtrace out of the crash dump?

cd /var/crash
gdb ./netbsd.0
(gdb) target kcore netbsd.0.core
(gdb) where

					- Bill