If you allowed the SP1 update to create an uninstall folder, you can use Control Panel / Add/Remove Programs to uninstall the service pack.
You can also open a CMD prompt and switch to the \%systemroot%\$NtServicePackUninstall$\spuninst folder. Then type spuninst.exe.
NOTE: If your system drive letter has changed, see tip 2596.
Before you uninstall SP1, be aware that programs that require SP1 or pre-sp1 hotfixs may not run after the uninstall.
If you installed any programs after installing SP1, you may need to reinstall them after the SP1 uninstall.
NOTE: If you performed a slipstreamed install of SP1, it can not be uninstalled.
NOTE: Uninstalling SP1 will back out any system updates performed by the service pack install.