Firstly, is it actually the Administrator account who's password you need reset or a user account with admin rights?
Often XP is setup with a user called say, Paul, who IS an Admin but not THE
Administrator. You turn the PC on and the logon screen shows Paul, whose account is password protected. However if you hit Ctrl+Alt+Delete 3 times at the logon screen it will change to the other style of entering the full username and password. If you enter Administrator as the username, and no
password, Often you can get in that way.
However if you really do need the Administrator password reset, look into something called Hiren's Boot Disk. If I remember correctly that can reset
passwords, as well as do a hundred other cool things.