i've had a recent confirmation that NetBSD-current boots properly on the
PB 520, though if you have a 68LC040 (no FPU) machine, you will still have
problems with the floating point emulator causing random core dumps and
the occasional panic.  (the latter happens if it's the init(8) process
that dies, of course.)

anyway, i suggest that you try a recent snapshot.  the kernels that use
the direct ADB driver should work, at least as far as getting to
single-user shell prompt.

--scott