I think I found the source of my problems.  I put a SCSI drive on the machine
and reinstalled from scratch (using the same ISO image I originally started
with), and then compiled a new -current kernel, which worked fine.  I copied
that working kernel onto my original IDE wd0 drive and it failed.

  I ran "dd if=/dev/rwd0c...." and these errors popped out.  I never saw any
errors during my previous debuging attempts.

wd0c: error reading fsbn 6799968 of 6799968-6800093 (wd0 bn 6799968; cn 6746 tn 0 sn 0), retrying
wd0: (uncorrectable data error)
wd0c: error reading fsbn 6799968 of 6799968-6800093 (wd0 bn 6799968; cn 6746 tn 0 sn 0), retrying
wd0: (uncorrectable data error)
wd0c: error reading fsbn 6799968 of 6799968-6800093 (wd0 bn 6799968; cn 6746 tn 0 sn 0), retrying
wd0: (uncorrectable data error)
wd0c: error reading fsbn 6799968 of 6799968-6800093 (wd0 bn 6799968; cn 6746 tn 0 sn 0), retrying
wd0: (uncorrectable data error)
wd0c: error reading fsbn 6800066 of 6799968-6800093 (wd0 bn 6800066; cn 6746 tn 1 sn 35), retrying
wd0: (uncorrectable data error)
wd0c: error reading fsbn 6800066 of 6799968-6800093 (wd0 bn 6800066; cn 6746 tn 1 sn 35)wd0: (uncorrectable data error)

  How do I determine which file occupies "6799968; cn 6746"?  I know I need to
ditch the drive, but first I want to find the piece that's most responsible for
my aggravation and grind it under my heel a few times...