1, You can press ctrl+alt+del on the logon screen and login as Administrator - this is the basic admin account and you have 9:1 chance it is not password protected.
Then go to control panel > users > his account and there is a option to reset password or you can add your own account.
2, format the drive and reinstall the system - this kills and sweeps about all tracks of the last user.
3, HiRen's Boot CD has some password recovery tools - you can use those too...
A little piece of advice>
Do this only if the laptop is legally yours and you have all legal rights to do so (and/or if you're too lazy to reinstall the OS like I am). If you want to crack someone elses laptop (e.g. your GF - to find out she's cheating) you might end up doing more harm than good (And you could end up in jail and/or pay a hefty fine too)