I figured out a way to do this using Address Book without resorting to Word or Print Shop. What I did was select the contact I wanted to use to print return address labels -- the same address printed on a page of 30 Avery labels (8160) -- and drag it to the desktop. I selected the resulting vCard on my desktop, clicked the right mouse button (CTRL+mouse-click if you have a one-button mouse) to get the context menu, and selected "Duplicate." I duplicated this one vCard 28 times. I then imported the 29 vCards back into Address Book, but I chose "Keep Both" when the Duplicates warning asked me what I wanted to do. I made sure to check the box "apply to all." I then selected these 30 contact cards (all of the same contact), and selected "File / Print" from the menu bar. In the Address Book area of the print dialog, I selected "Mailing Labels" from the Style pull-down menu. Then I clicked on the Layout tab and selected Avery standard and 8160.
In order to save myself the trouble of having to do all this over again, I selected Save to PDF from the PDF drop-down menu at the bottom left corner. That way, I can print out these return address labels any time. After all that, I deleted the extra 29 copies of the contact.
I know this wasn't as easy as doing it in Word, but if you don't have Word and don't want to buy extra software, this is how to do it with a standard installation of Mac OS 10.5.