From Quickly Formatting Multiple Documents for Word 2007 (I hope that for Excel it may be somewhat similar):
- Display the Developer tab of the ribbon and then click on the Document
Template tool. Word displays the
Templates and Add-Ins dialog box.
(Click here to see a related figure.)
- Click on the Attach button. Word displays the Attach Template dialog
box, which looks very much like a
standard Open dialog box.
- Use the controls in the dialog box to locate and select the template
you want attached to your document.
- Click on Open. The Attach Template dialog box disappears and the
name of the template you selected
appears in the Document Template box.
- Select the Automatically Update Document Styles check box to make sure
that the styles in the template are
applied to your document.
- Click on OK.
If you don't see the Developer tab
necessary for step 1, then you need to
make the tab visible. You do that by
clicking the Office button and then
clicking the Word Options button. In
the resulting Word Options dialog box,
the Popular option should be selected
at the left. Make sure the Show
Developer Tab in Ribbon check box is
selected and click OK.
For older versions of Word, please see the above article.
You'll still need to open each document in order to use the above method.