Auto logon\login for xp and windows 7

[Therlow]

For Windows 7 below

Press the Windows key + R on your keyboard to launch the “Run” dialog box.
Type in control userpasswords2
Press Enter. The User Accounts window will display.
Uncheck the option “Users must enter a user name and password to use this computer”
Click “OK”
You will then be prompted to enter the current password and confirm it.
After doing so, you will no longer be prompted to enter your password upon login.

For Windows XP to tun on Auto logon
http://go.microsoft.com/?linkid=9746380
To turn off
http://go.microsoft.com/?linkid=9746382