Hi Mike,
For reasons known only to the wizards who built VBA at Microsoft, Word uses the special name AutoOpen, but Excel requires an underscore in Auto_Open. (More info here.)
Also, Excel doesn't have a direct equivalent to Word's AutoNew (which runs when you start a new document based on a template that contains that macro). You may as well delete the AutoNew macro from the Excel sheet and just leave it in Word. If you need that functionality in Excel, see this thread.