The nav bars are self contained wizards that aren't customizable.

If you have programming skills however and knowledge of Office VBA you can
build your own nav bar. There is an article available at
http://www.msdn.microsoft.com/office/understanding/publisher/articles/default.as
px?pull=/library/en-us/odc_pb2003_ta/html/odc_pb_navbarswebpubs.asp