Impromptu, Can not add new tables?

Hi, all:

I opened an existing category as user class creator and try to modify
this catagory by adding 2 more tables and Joins.

But on Catalog--> Tables --> Edit tab
the buttons "ADD-->" and "ALIAS-->" are grey.

I checked user profiles--> Govornor, I have Edit Folders checked.

Is there anything I did not know about? How can I add new tables to an
existing catalog? This catalog is created by somebody else, How do I
know is it a distributed Catalog?

Thanks a lot

-rockdale