Tabbing through form fields
 

I am in the process of creating a form that will be used by many people who
are almost computer illiterate. It containts drop down lists, and check
boxes, as well as cells where data needs to be typed in. I've successfully
locked the form so that only the necessary fields are available.

I want to be able to tab through the form, advancing to the next field that
requires data. Currently, the tab will only take me through the cells that
I've unlocked that requires data, but won't jump to the drop down menus or
the check boxes. Is this possible, and how?