Thanks to all the people who responded.  For the record, I turned all the
Plug-and-Play settings off in the BIOS, but the problem was NOT solved.

> > dmesg shows:
> > pciide0 at pci0 dev20 function0: OPTi 82c621 PCI IDE controller (rev. 0x11)
> > pciide0: bus-master DMA support present, but unused (couldn't map registers)
> 
> This seems to be a problem with the early revisions of the OPTi controller
> not being true bus-master devices.
> 
> A workaround is in -current but didn't quite make it under the wire before
> 1.5.1 was frozen. You've just reminded me that I need to submit a pullup
> for 1.5.2. ;-)

Thanks a million, Steve.  In my research of the motherboard, I recollect
seeing mention of the bus-master deficiencies of the chipset.

Are there a lot of changes to be made?  If it is just a matter of patching
one or two files (or replacing them with current ones) and then recompiling
the kernel, I'd like to give it a shot.  I'd really appreciate brief
instructions on what files to patch/replace, and where to get the patches
or files, if it's not overly complex.  Thanks.

henry nelson