A friend had asked me yesterday how to reset their Windows XP password (by "their" I hope they meant on their own computer). There are several ways to do that. The 3 easiest ones are:
1) Hiren's BootCD: I know it's illegal to distribute, but if you own the program licenses then it's all yours, along with a lot of goodies!! The latest version is 9.1
2) Petro's way: A really good article giving you a lot of information
3) Techtrax way: Another article about the same topic, but if you tried the above ways, I believe you'd do it by now.
Enjoy your "new" password!