Looking at this a little closer, I think it will probably be hard, depending on what you really want to do.  I think it is doable, but not positive.

I've now looked into this a bit more in detail and I don't think it is possible to implement anything in this particular case. The combobox is a list box and my idea was to display a tooltip when the user moves the cursor over the dropped-down items that gives a description of the item as a help before selecting an item. But I realise that there are no events available to catch the user's cursor movements. But I guess after selecting an item a tooltip could be displayed as an alternative. My question is, does Windows generate any events for the cursor movements that could be added to ooDialog?