Browsing around the web, it seems your problem may be caused from an incomplete install or possibly from the Dell Support software installed on your computer. I would go to Control Panel-> Programs and Features and completely uninstall MS Office and any of the Dell Support software that you may find.
Then reboot, and go to http://support.microsoft.com/fixit/
, and try the Windows Update fix.
Then reinstall Office, and try to update to SP1. Post back here with your results.