So... I now have a copy of Win7 home Premium SP1 but it will only upgrade my Vista if I can boot to normal mode. I managed to boot long enough to get to the CD and run Setup. I get to Checking compatibility and it spends some time there, then tells me I have to boot from the CD. Frustrated, I nuked the drive and tried to do a clean install but it can't find Mass storage drivers either in AHCI or IDE mode. I'm sure that the machine is physically OK - it will run in Safe Mode for days, run Linux, etc.