Thanks, Shane.
The person I'd passed it onto has wiped the HDD and is going to try again and if the Bootmgr error reoccurs, is going to try the Bootrec remedial steps and if that's a no go, then see if the smaller ISO that JR has linked will install.
Unfortunately the computer vendor no longer supplies Vista OEM disks and the ones the guy has, are sticking after putting the second one in which could suggest it's damaged.