it seems to me this guy blagged it abit getting the job even i know how to do a clean windows xp as ive done it a few times and im not that experienced with computers but i can do simple tasks
ask your manager how to do it.
Ask the other guy how to do it and then go to the manager and tell him to fire you because you shouldn't be working in a computer shop if you don't know how to do something so simple.