did you get the windows XP disc with it?? if not then you are snookered, you can do nothing unless you can get the password.
all you can do is reformat the computer what type of XP is is it xp corp? if it si and you do not have the disc all you ahve to do is borrow someones corp disc to reinstall but use your own product key that way you are not doing nothing wrong. to find your product key ther is a cool little tool made by a Russian it is called
view/key xp i have it on disc it is cool.
or download
THIS KEY FINDER