I was assuming that the desired behavior was

1. listbox
   
2. not a permanent appearance of the description, but the default tooltip behavior - have to move the mouse, goes away when you do something else, etc.
   
3. an item in the list would have to be selected - arrowed to or clicked - to change the tooltip

With that in mind, it works. Not the best thing to do, but it meets the assumed requirements.

However, what I should have said was:

Don't do it that way, use a 2 column combobox instead.

Another problem with the tooltip is that it may hide the other information.