How Site Navigation Settings Work
If you have deployed SharePoint Server 2010, the navigational options via the Web interface are quite extensive. They include options to add new links and headings, manage existing links (including link sort order), modify and hide existing links, as well as set the number of dynamic fly-out, or drop-down, links. Additionally, if your site has publishing enabled then navigational inheritance is automatic. However, if you’ve deployed SharePoint Foundation 2010, then options to customize navigation via the Web interface are somewhat limited and you need to instead use SharePoint Designer to address navigational customization such as dynamic menu drop-downs and fly-outs.