This applies to any Microsoft Office 2007 “recent document” list. You do, of course, know that by hitting the Office Button (the “marble,” the magic button, the round logo at the top left), you can view many useful menus including the Recent Documents list? (In previous versions, it was under the File menu.) This is a very handy shortcut to pull up the last few documents you’ve viewed in Word, Excel, Powerpoint, etc.
Office 2007 has really improved this little feature with the ability to “pin” something there permanently. If there is a document you don’t want pushed down to the bottom or dropping off of this list, you can click on the little pushpin icon to the right of each document title. This will keep the document on the list permanently, thus providing you a quick and handy shortcut to your most-used documents.