Navigation help

Hi,

I'm building an Intranet for a charity i work for using asp and some web wiz applications. The problem i am having is i want to create a navigation system that has different options for different user depending on what user groups they are members of on our domain using Windows Server 2003/IIS 6 o our server. E.g An administrator would have more options than a guest. I was hoping to use a series of include files.

Can anyone point me in the right direction?