I needed to set up a few machines for a client in an internet cafe type scenario, but the client provided me with computers that had been added to the domain. The domain had a password requirement which meant I could not configure the default login on the cafe machines to have no password.
To reset the domain policy without adding the computer back into the domain and actually changing the policy for a short while you can reset the security settings on an XP computer to that at install time using the following command:
secedit /configure /cfg %windir%\repair\secsetup.inf /db secsetup.sdb /verbose
This resets lots of settings back to the default installation configuration, but meant that I did not need to reinstall the operating system.
For full details on the limitations of the above command see http://support.microsoft.com/default.aspx?scid=kb;en-us;313222