I've just spent 20 minutes trying to find a power supply to replace the one for my network hard disk, which I thought had died after I accidentally unplugged it.
Then realised that unlike its predecessor, this drive box fails safe by staying switched off until you press the on button again. Not quite so convenient, but probably a lot better for the hard disk.
After struggling with the HP mini-note and failing to get wireless networking working for more than a couple of minutes I eventually sent it back to eBuyer. They just emailed me to say that it really is faulty - not just my incompetence. They're also out of stock and can't give me any sort of delivery date for a replacement.
In view of this, and my realisation that it probably isn't an ideal machine for my purposes anyway, I've decided to go for a refund instead. While I do want something small, a netbook probably isn't my ideal solution; not sure what is, to be honest, probably something between a netbook and a PDA with a keyboard, but faster and a better screen and more memory than the HP 720. I really wish that someone would build something like that into a form factor say the size of a DVD case.
Many thanks to everyone who helped with this, especially to all those who helped me come to the realisation that it really was faulty - it's a shame it didn't work out, I shall try to think of it as a learning experience.