Question about Removing a Program?

I've acquired a computer, no longer in use, which actually includes Windows Vista. The problem however is that the computer is password access other than guest which disallows much of it's useful value.

I'm not interested in an opinion regarding Vista, just any suggestions of the possibility of making the comp. a viable, workable piece of equipment for me.

I can have the drive formatted and install my version of XP, but I'm looking for other alternatives.