How to Disable the Windows 7, Vista and XP Startup Password
If you do not wish to secure your computer with a password, Windows 7, Vista and XP include an automatic log-on feature. This feature allows you to log into your computer without entering a password each time you boot.
Navigate to the Advance User Account Control Panel. Click the "Start" button and go to the "Search" box. This will bring up the User Accounts window.
Type "netplwiz" or "Control Userpasswords2" into the "Start" button search box and click "Enter".
Uncheck the option that says "Users Must Enter a User Name and Password to Use This Computer." The click "Apply".
Confirm the current password and restart your computer.