In Windows XP Home Edition you can assign a password to your user account to prevent other users from logging into your profile. If you have teenagers at home, they have likely done this on their own accounts to keep mom and dad from snooping. However, in most cases, these passwords can easily be removed.
To remove another user's password, your own account must be a "Computer Administrator" acount, not a "Limited User". Click on Start, then Run and enter nusrmgr.cpl into the box and click OK. This will open the User Accounts Control Panel applet. Here you will see all the user accounts on your PC. Click on the account that you want to remove the password from and then click on "Remove the password". You will have to confirm by clicking the "Remove Password" button.
Now you can log off of your account and login to the other account with no password to keep you out.