dropdownlist help

Question

I have a booking form for a travel agency where there are two dropdown, one to select the package representing a state and the other to select the subpackages belonging to that state.......... how am i supposed to connect both these dropdown so that when i select a state package from the 1st dropdown list only the respected subpackages of that state package are shown in the other...... also please help me out with the database for this... if any... Thank you.