try this
go to start menu -> Run...
in the dialog box, type "control userpasswords2" without the quotes (just copy and paste)...
uncheck the checkbox "Users must enter a username and password to use this computer"... and click "Apply"...
once you have done that, a dialog box will prompt you to enter the username and password (the account you want to login automatically)... if you dont have a password, just leave it blank... then click "Ok"...
see if it work...