Are you talking about the Places Bar in the left side of the Open dialog
(for example)? What version of Office? In Office XP/2003, navigate to the
folder you want to include, and select it (i.e., show it as selected within
its parent folder), and choose Tools - Add to My Places. To change the
position of items within the Places Bar, right-click and choose Move Up or
Move Down.
Note that the default places can't be removed. But, they can be moved to the
bottom so they're out of the way. Note also that by using Small Icons, you
can fit a whole lot more onscreen without having to scroll.
In Office 2000, there's an add-on that can help you manipulate the placels
bar. See here:
http://www.mvps.org/word/FAQs/Customization/CstmzeWd2kOpenSaveDlgs.htm