Well I quite enjoyed building the computer, inasmuch as it is built (some inessential bits not added yet). And it's not dead and you can get into the BIOS setup and it can see its drives. But it won't boot from either an Ubuntu Live CD or a Linux Rescue CD or a Windows 98 boot floppy. Booo. (At the point where you'd expect those to be happening, the CD player does spin up but doesn't light up its "working" light, for what that's worth, and the floppy doesn't make vvv vvv noises either.) Tried different CD player, same thing.
More experiments tomorrow I expect. Any bright ideas v welcome.