>I am using a comboboxx to allow users to choose a category to display. The key reason for this is the box's incremental search feature. The problem is, even after setting focus on the box, you can't use the incremental search until after clicking the box with the mouse. Is there a way to automatically open the box and prepare it for Isearch?

If your have drop-down list (combo.style=2), incremental search will work immediately. In drop-down combo (combo.style=0) user can type in upper section, so incremental search is irrelevant during the typing.