Hi Luar,
I am trying to understand this more clearly. Do you wish to add more(new/diferent) types in the object type picker ? Object type picker is the picker that is launched when you click on 'Add' link on the search page.
The objects that you can currently see on the object type picker is driven by a preference called Site-->Utilities --> Preference MAnager --> Search -->'All Applicable Object Types'
If you could give more details and what you are exactly looking for, I will be able to help better.
-Malavika