Have the Search box in the Navigation Bar autoexpand when used
The Search box in the Navigation Bar at the bottom of forms is a pretty small area -- sometimes tiny, depending on the size of the form. And if you use a Navigation Caption, it's even smaller still.
When the user clicks in the Search box, it should auto-expand, making the scroll bars next to it temporarily shorter and the Search box longer, until the user is done with the search. Then it can go back to normal.
Alternatively, it could be replaced with a small pop-up that appears when the user clicks in it. But just increasing the size of the box should be sufficient.