I'm assuming you are using menus in Word 2003 or earlier, if you use Word
2007, the process is basically the same but involves use of the Ribbon.
Insert a section break (Insert, Break, Section break, Next Page) before the
last page. Then view the footer of that last page, you will notice you are in
the footer of section 2 (or higher if you have more sections in your
document) and on the Header and Footer toolbar, click Link to Previous to
break the link with the previous section. You should now be able add a footer
to this section without changing earlier sections. You can type text, or use
icons on the Header and Footer toolbar to insert an automatically updating
page number and change its number format or starting number.