You don't have to add a header to every Excel worksheet individually when you can group them first.

Click the "Insert" tab. Click the "Header & Footer" button on the ribbon. The spreadsheet zooms out slightly and the "Click to add header" text box opens at the top of the spreadsheet. Click into ...

In Word and Excel 2007, it’s even easier. Go to the Ribbon and click on Insert and then on the Header or Footer icon. Then, to select the graphic, click on the Picture icon, which is to the left of ...