Warning: Security Risk
1) click Start and type ‘netplwiz’ or click that name on the Start menu
2) in the GUI window that comes up, uncheck the “Users must enter a username and password
to use this computer” box
3) click ‘Apply’
4) in the new dialog box that opens type the name of the account you want to auto-logon by default (if the account is not normally passworded then it blank)
5) click OK and exit.