Any ideas on how one could add a page to a site which would then be able to be displayed on all portals on the install?

Sebastian,

Do you recall the names of any such modules?

Thanks 

All i'm finding is modules that provide shared users between portals

My Idea is as follows:

Have a master site with some Tabs (pages) with some content

scenario 1

Share the content to subscriber portals by somehow allowing them read the tab from the DB of the master site. Think of how the Host menu is in the Tabs table once - and it is shared between portals. Or even how the Admin menu gets put into each install - I want to know those processes - this is open source - right?

scenario 2

Have a master site with a tab containing content thatyou want to display on child portals. A SPROC that will copy the tab and all content from the master and do a cartesian join on the subscriber portals then insert into those (subscriber) portals an exact duplicate of the master. The problem here is again - the DNN documentation

Thanks To all who share thier ideas