Thanks, V. Mr. Clod's been in front of it all day, fortunately making progress. As it turns out, the problem ultimately seems to have been just with the boot drive, as he was able to boot into an existing Windows install on a different drive with both motherboards without a problem. At this point, all the pertinent data has been recovered over to the replacement drive, everything's running happily, and the old drive is just going to be trash--he did make an attempt to format it, but it started spewing errors and he decided he didn't need a piddly old 30-gig SCSI drive anyhow.
