When I've seen that sort of problem, it's generally been because the
BIOS PCI bus speedup settings were too agressive.   The speedups are
generally not useful for NetBSD, AFAIK, and they wind up causing
errors on the PCI bus from time to time.   The symptoms you describe
are exactly those that we were experiencing here at Vixie Enterprises
with our Pentium II motherboards.   When I disabled all the PCI bus
speedup hacks in the BIOS, we completely stopped seeing hangs on the
bus.

Unfortunately, I don't remember the names of these options off the top
of my head, but if you go into the BIOS at power-on time and look
through the menus for chipset settings, you should find some settings
for PCI that sound like they're speed hacks.   Disable them all.
Your problem should go away.

			       _MelloN_