I compiled with DDB, and no pseudodevice.  It compiled and
(surprise!) runs.  The FAQ says hit control-alt-escape to get into
ddb...but that didn't work for me.  I played for a while, and at last,
success.  This is cool.  Thanks!

The stuff that needs to go into the FAQ:

If you want to use ddb, do NOT use the pseudodevice.  Just 
add options DDB, and options SYMTAB_SPACE=70000 (or thereabouts)
and recompile your kernel.

Then run dbsym netbsd.

Then reboot using that kernel, and enter ddb when you want to with
control-alt-escape.