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 /verboseThis 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