Tab to combobox and select it instead of the cell
 

I have a worksheet with several combo boxes and the work great as far as
typing in the first letter and it auto completing.
My problem is, many of our users want to "tab" to the next field, and they
get in the field, but they don't actually select the combo box until they
mouse click on it.
Is there some way I can set this so that they can tab to it and actually
select the combobox instead of the cell behind it?
Thanks for any help you can give me