Didn't you have an option to keep changed files during the service pack install? I'm guessing since you asked how to uninstall you must have said no during the sp1 install. If so, then you are out of luck and will have to re-install or restore your server from tape backup if you have a backup prior to the sp1 install. But, re-installing the OS is the better solution.
You could also try installing sp2 of TeamSite 6.5 as it is supported with w2k3 sp1.Thxs,Mohammed Gazal.