1. Click Start and then select Run,
2. In the Run window, type control userpasswords2, and then click OK button,
A User Accounts windows pops up.
3. Clear the "Users must enter a user name and password to use this computer" check box, and then click Apply.
You will be requested for the username and password of the account you wish to automatically logon as for following reoots of your system.
4. In the Automatically Log On window, type the required information and click OK to close the window.
5. Finally click OK to close the User Accounts window.
At any later stage, you can activate this security feature by following the same steps but recheck the box, at step 3.