It is no problem, I always recommend when buying a used computer to remove the partitions from the previous users, create new partitions, and install a fresh copy of windows. This will save a lot of headaches in the future.
I sale a lot of used computers, and when my clients get one, those steps have already been done, I have it where when they turn it on, it is at the welcome to windows now lets set it up screen. Just like if they bought it new from the factory.
Also, for XP here
is a better place to get questions answered, some of us are pretty well knowledgeable with XP, but this is a Windows 7 forums..