I've written the whole thing up in a bit more detail, although there's nothing about the software set-up process (might add that if anyone asks). It's on my ancient blueyonder personal web page here, which also shows an intermediate stage with a USB hub and 4 flash drives that I never got around to mentioning before:
Erm, edit: Blueyonder (i.e. Virgin Media) have scrapped their users' personal web sites, so this no longer exists. -I.N. July 2020.
http://www.ian-nic.pwp.blueyonder.co.uk/PiFi
Oh, and it now has a new, glowing badge.
http://www.ian-nic.pwp.blueyonder.co.uk/PiFi
Oh, and it now has a new, glowing badge.