How to customize PortalDetailed Navigation like Left-hand navigation in SDN

Hi,

I would like to customize the detailed navigation in our portal similar to the left-hand navigation in SDN Community home page (http://www.sdn.sap.com/irj/sdn) with similar tree like navigation.

How can this be done? Being a newbie, any sample code or starting point will be very helpful.

Thanks,

Ajay