An addendum: Crikey, I don't know if I should format the little 100mb System Reserved partition. I assume if I want a truly clean install I should format this and drive C.
I've never considered this point before.
Double crikey. I've just been reading that W8 needs 350mb for that partition. Mine is 100. I wonder if the setup will alter that, though I have a feeling it should be dispensed with and a format of the full C partition done prior to the instal - that 100 partition must have been made automatically by the W7 instal and I'd guess W8 would seize 350. But it's a guess.
Also, some folk copy the W8 files onto another USB stick. When the system fails to find files, they direct it to look there.