Windows Server 2003 SP1 is a very good security update released by Microsoft and I hope many of you would have already installed the same.
However, if for some reason, you had to remove the SP1 then you may no longer be able to browse ASPX Pages.
Even after you enable the WebService Extensions from IIS, you will get a 403.1 Error message and will be unable to execute ASPX Pages.
The resolution for the same is to uninstall and reinstall the IIS.
That should resolve the issue.
Cheers and Happy Programming !!!