Be very careful here...

Start/Run/type "regedit" - click "yes" in the UAC box

Navigate to HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/

Find the Office folder and delete it. You should do the same thing in the HKEY_CURRENT_USER folder as well. This will completely remove office from your system. For best results, go to Add/Remove Programs and run the Uninstall for Office first.