That navigation bar is only meant to display Topic areas; any new top level Topics automatically gets a link to it put into that bar. There's nothing stopping you from using Front page 2003 to add a static link to whatever you want "around" that bar.
There's a million-gazillion ways to help users get to a particular WSS site: the Links For You web part on the main portal page (and the similar one in My Site for using Add To My Links), custom Links lists, any HTML/Rich Text web parts, use the Favourites in Internet Explorer, drag the shortcut to the desktop, etc. etc.
The best method: the existing Sites Directory. Why reinvent the wheel? It's only one click away...