Correct Use of ComboBox

Question

I'm trying to think about a better interface for a combobox and grid control that I have in WinForms application. The combobox is used a search box to find Tenants that we have in a database. A user is then able to add the selected tenant to a grid with a button. It looks a bit like this:

If a user doesn't select a tenant, but enters their own text, a new tenant will be created and added to the grid and the Tenants table in the database.

Users have been asking to see more information in the combobox before adding a tenant to prevent duplicates (We have many variations of WalMart that I didn't think were possible). I can control the number of columns that are displayed in the dropdown portion, but I'm starting to think this isn't the best interface.

My screen space is limited. I have to plan for 1280x1024 monitors and some of that is already taken up by window bars and menus. The picture is about how much space I'd like to take up. The rest of the form is already very cluttered and users don't like having to scroll the larger parent form.

So a popup window with a better search interface is starting to sound nice but I'm also afraid of messing with the users' workflow. What's a good way to tackle a one-off search/add feature like this?

Answer 1

What's the minimal pieces of info a user needs to identify they have selected the correct item in the dropdown? Say it's two pieces... consider something like this:

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By putting in the add action as the last item within the dropdown, you force the user to do an initial search before creating something new. Not sure whether this is something that's easy to build though.