Computer is a go!
Turns out I did have the IDE cable plugged in backwards (thanks go to streamlinedata for the tip off). Silly me. Silly manufacturers making it possible to plug it in both ways... After many hours up to my elbows in computer bits, and on an endless search for drivers, the computer is functional again. Now all I have to do is catchup on the week of livejournal flist reading that I've missed, and restore my porn from the backups.