if...then statment in Acrobat

I need to create an if...then statement in an Acrobat 8.0 form. I have a drop down menu for one of the questions and if you select the first option, I want it to then promt the rest of the drop down menus to be mandatory to answer. If you select any of the other options in that first drop down section, the rest of the drop down boxes should not be mandatory. I don't know enough about javascripting to code the conditions correctly. Could you please help me?
Thanks.