I need to know how to create a conditional form. For example When I select Truck on the first drop down menu "vehicle type" the second drop down menu "model" only shows models of Trucks instead of showing the models of all the cars, SUV tans, etc.

Try searching in UA for Cascading Combo Boxes. This is an often asked question.

This article has the answer I think you are looking for...

hth,
Jack