Thanks for the tip. It was a bad ISO. I got another, burned it, and I'm ready to roll.
Oh no I'm not. What I burned has files/folders and setup.exe, all with 0 bytes. I downloaded from Mininova, using my GetRight download manager set as default for bittorrents, but it's not a procedure I'm used to. I somehow managed to download/burn the 7000 beta, so I know it's possible, but I've lost track.
This is obviously not the right forum for advice on how to download bit torrents, so I'll look round online and see what advice turns up.