and another method:
Disabling Windows XP startup login prompt for password
1: Click Start, and Run
2: Type "Control Userpasswords2" and press enter.
3: Uncheck the box for "Users must enter a user name and password to use this computer."
4: Click Apply and Ok.
Disabling prompt for password after Windows XP resumes from standby or hibernation
1: Click Start, Settings, and Control Panel
2: Double click Power Options
3: Uncheck the "Prompt for password when computer resumes from standby" option.
4: Click Apply and then Ok.