I've just tried the 3.5 version installation again... and it went without a hitch!!!
I've just built a new computer using an Asrock Extreme4-M m'bd and an Intel i5-3450 cpu which runs superbly.
I don't know why the previous times were a problem; it got through to asking which control interface I wanted, either Windows or Commander and then said something about unable to complete installation and removed all the files!
Anyway, now I can proceed to use it.