You could do this by creating two of the same named pages..

You set permission for one to be unauthenticated, so only those who are not logged in or registered will see it, and when they click it - it takes them to the login/register page.

You then create another page with the same name, with your permissions set for only registered users to see it. Then as they log in, it's same switched over to the right one.

This might cause a bit of congestion on the menu when logged in but that will resolve the issue of wanting a register page to happen.

OR  you could do it this way -

Set the page for everyone to view -

Set the permissions on the modules - so that only registered users see the content. And then place the Login or Registration information on the same page but set for Unauthenticated users. Either way, it should work. 

Hope this gives you ammunition!

Nina Meiers