I switched to sbc kernel (GENERICSBC-9), and got my machine to boot in
single user mode.  While it was booting is gave numerous parity error
messages, does anyone know what this could mean?

After booting in single user mode I ran fsck -f /dev/sd0g a couple
of times.  The first time through produced lots of errors,  subsequent
runs of fsck produced warnings about 2 unreadable blocks.

After booting into multiple user mode, I got additional medium error
messages.  

I rebooted the machine into MacOS and ran the test function of Apple's
HD SC Setup program.  (The same one I used to partition with).  It
said there were errors on the disk that could be fixed by initializing
the entire drive.  Is there any way I can initialize the usr partition
without affecting my MacOS partition?  I don't want to restore my
MacOS partition if I can help it.  Would recreating the file-systems
on the root and usr partitions fix the problem?

TIA,
Alan Bindemann