Windows 7: I can't log onto windows on a laptop I was given

My Mother bought a Dell laptop Latitude D600 with Windows XP. She hasn't used it for over a year and can't remember her user name or password to log on. When the computer is turned on and goes to windows log on it just shows pre-install. Would there be any way to log on?

If it still has Win XP on it, and maybe even if Vista, hit Ctrl+Alt+Delete keys twice and you should get the Win 2000 type log on screen. Type in Administrator in the User name box and leave the password box empty then hit the enter key.