Excel installs new features at each launch

Since reinstalling Win2K and Office XP, each startup of
Excel results in the Installing Microsoft Excel Components
dialog and the progress bar indicates something
significant is being read into memory.

At installation, all Excel features were either completely
installed or made unavailable. There are no files in any
of the Excel Startup folders in Documents and Settings
folders. Under the General tab of the Tools|Options menu
the File Locations entry is blank.

Which features are being installed and how can I stop this
behavior?