Anyway, I've now had enough. I was planning to use the recovery CD to restore it to factory settings, then stick it on Ebay (starting price of £1 + postage), but that's not really practical in it's current state. Instead, I'm going to write this off as an expensive mistake, and treat it as a sunk cost. My new priority is simply to get rid of the thing, so that it's not taking up space.
So, I'm now offering this free of charge to anyone who wants it. (Full spec.) If you're interested, let me know; if not then I'll stick it on Freecycle, and if nobody bites there then I'll just take it to the recycling depot.