By inner navigation I assume you mean the Inner Navigation user control implemented in the TIU site. If so, it would be best if you could take a look at the code of this control which is located under Sitefinity 3.0\TIUSite\UserControls\SideNavigationL1.ascx
. As you can see, there are only one SiteMapDatasource control and a panelbar which is connected to the SiteMap control.
Of course, you could achieve this without making a user control. You could just drop a SiteMap and a RadPanelbar control from the toolbox while editing a page or a template via Sitefinity and connect the panelbar through the DataSourceID property. You should set these SiteMap properties ShowStartingNode="false", StartFromCurrentNode="false", StartingNodeOffset="1" and this Panelbar property too: Depth="1".
Let me know if there are any problems.