How to: Share the Top Link Bar Between Sites
In Windows SharePoint Services 3.0, you can provide users a consistent navigational experience across sites by specifying inheritance from the parent site, which is especially important when you need to provide navigation between peer subsites. In this case, each subsite created under the site shares a top link bar and is itself represented among the links. Without navigational inheritance, each site would have its own navigation. Shared navigation must be implemented through the top link bar of the parent site.
Sharing a top link bar across sites simplifies the user experience because it allows easier cross-site navigation. Shared navigation simplifies navigation, but it should not be a replacement for careful planning. Understand that the shared navigation control represents a "flat" site structure and could possibly confuse users about the actual hierarchy of sites created within a site collection.
You can implement a shared navigation control between sites within a site collection through the user interface. You can specify to share the top link bar either as you create each site or after you create each site.
To add the top link bar of the parent site to a subsite while creating the subsite
As you create each site, in the New SharePoint Site page, select Yes for Use the top link bar from the parent site in the Navigation section.
To add the top link bar of the parent site to an existing subsite
Click Site Actions, and on the pop-up menu click Site Settings.
On the Site Settings page, in the Look and Feel section click Top link bar.
On the Top Link Bar page, click Use Links from Parent, and then click OK in the message box that opens.