Just because you create a document on a certain size paper doesn't mean your final document must be printed on that size paper. Further, it doesn't mean you'll have to do fancy maneuvers to switch paper size. Word offers a scaling feature that will allow you to scale your document to a different paper size. While it is quite easy to do, the option is not easy to find unless you know where to look.
For instructions on scaling your Word 2003 document to a different paper size, keep reading! I also have step-by-step instructions for scaling your document paper size in Word 2007.