Taken from:

http://support.microsoft.com/default.as ... -us;315231

You can also use turn on automatic logon without editing the registry in Microsoft Windows XP Home Edition and in Microsoft Windows XP Professional (not joined to a domain). To do this, follow these steps:
Click Start, and then click Run.
In the Open box, type control userpasswords2, and then click OK.
In the dialog box that appears, click to clear the Users must enter a user name and password to use this computer check box, and then click OK.


I hope that helps.