This is the Index Page
This is an iFrame containing the scrollable menu.
This is another iFrame named "display" that contains the page selected from the menu.
The iFrame above contains a page called "menu".

For the links, set the Link Type as "page"

Set the Link URL to the appropriate page.

In the code, enter:-

target="display"

Changing "display" to the name of the iFrame wher you want the page displayed.