The long sad saga of my "rebuilt" PC has come to a happy conclusion, although not what I thought it would be at first. The new motherboard is in and the machine runs beautifully. With DSL installed and the router doing its routing thing, life is good. It turns out that I may have waited to long to upgrade, as I wound up using a lot fewer of the old components than I had anticipated. Anything with an EIDE interface (except drives) was out -- PCI slots only. I had to solder together a new switch and wiring harness -- the old box used AT, while the new power supply is ATX. I had to "carve a new orifice" in the backside of the chassis to put the motherboard in -- they had put a pretty good sound card on the board, with the output jacks sticking up above it. Most oddly, there are no serial, mouse, or parallel ports, so I had to spring for a new USB keyboard and get an adapter for my printer.
On the other hand, the damned thing screams.
Better yet, I haven't yet set this one on fire