Your options are pretty limited, as the source code is not included in the code you get access to. About the most you do is hide certain buttons and add others (both with JavaScript). The buttons you can add are limited to, say, navigating to other pages. You can't (to my knowledge) re-create the drop-down functions of the friends or message areas.
You should also be aware that the Ning bar is one of the areas that is slated to change in coming releases, as functions are moved out of the Ning bar and into the network proper (so it would become part of your source code).
I too would like to keep only the messaging functionality and friend request acceptance/request stuff but I can seem to find a css/display option that allows just these 2 functions. Is this possible? How?
Or do I have to wait until these are moved into the source code that we are given? If so when?
Go to Manage -> Appearance -> Advanced, and enter this CSS:
#xn_bar #xn_bar_menu ul li { display:none; }
#xn_bar #xn_bar_menu ul li#xn_messages,
#xn_bar #xn_bar_menu ul li#xn_friends { display:inline; }
The first line says hide all the list elements in the Ning Bar navigation.
The second and third lines say show the list elements called xn_messages and xn_friends.
If you change the order of this code, it won't work. If Ning change the HTML markup of the Ning bar it won't work.