Looks like you want to use the navigation inheritance, this article will shed a little more light and hopefully point you in the right direction:
http://weblogs.asp.net/soever/archive/2006/05/31/SharePoint-2007-navigation-dissected-_1320_-part-1.aspxI often use a custom navigation provider and a sitemap.xml file to keep the navigation consistent across the site, this does have a maintenance overhead of keeping the map up-to-date though, so not good for volatile sites.
Andrew Carter
.Net & SharePoint