The results are going to be unknown and we'll never be sure it worked out.
"will it erase all user files?"
You don't know till you try but did you just tell us you don't have a backup copy?
I have a system that had a windows xp evaluation version (pirate) that is expired, I would like to install vista. First question: can I just upgrade to vista even if windows xp is expired? Second question: if I install vista from scratch, will it erase all user files?