Well, the death throes of whatever died in the old computer took out both disks on the IDE chain, and the controller logic. Unfortunately, one of those disks was the /home disk. Lots lost :( I hadn't noticed, but my dodgy backup methodology had missed my .ssh and Mail directories. Ouch.
I'm now sitting in front of a very quickly thrown-together new Athlon system (the minimum spec system I could buy - 1.9GHz would you believe) which replaces the old, now very dodgy, hardware.
The moral of this story ... more regular, complete backups!
While I was at it, I splurged on a Linksys router/switch to take over that role from my desktop. AU$169 well spent, since it's quiet, compact and consumes significantly less power than a real computer :)