I'd start by repairing Office. This will restore missing files, and re-register Office dll's:
Do this:
Method 1
On the Help menu in any Office program, click Detect and Repair.
Click Start.
To restore program shortcuts to the Windows Start menu, make sure the Restore my shortcuts while repairing check box is selected.
Method 2
Double-click Add/Remove Programs in Control Panel.
Double-click the Office 2000 entry listed in the Add/Remove Programs dialog box.
Click Repair Office.
Click either Repair errors in my Office installation, and then click Finish.
Be sure to select the Restore my shortcuts check box again.
Good luck,