<select> changes according to previous choices

Hi experts
I have got three <select> boxes. The subjects in the boxes changes according to the choices the user makes in the previous <select> boxes. That seems to work all right up till now. My problem is as follows:
- Is ‘Choice 1’ chosen from the first <select>, the user automatically needs to continue to box two and three. – But if ‘Choice 2’ is chosen from the first <select> the second <select> has to be ignored and the user is send directly to the third <select> box to make the last choice.
Can this be done, and how? I’m not that experienced at JavaScript, so please keep it simple ..

If it helps, take a look at my testform here (http://www.larsliin.dk/test.htm)

Why not give just one choice for #2?

I imagined that when the user chose the option from the first <select> that brings him/her directly to the third box, the second box would say ‘-No choice-‘ or something similar. That way the user wouldn’t get confused when there’re suddenly no options in the second <select> box. Do you see what I mean?

I know what you are asking for. Can you answer my question? What's wrong with just giving them only one choice in the 2nd select?

Well, I want the options in the third <select> to change automatically according to the changes made in the second box, which again have changed accordingly, to the first box. What I mean is if I do what you suggest, can I make the options in third box change accordingly to that one choice that the user are given here? If so, that might be what I’m looking for ..
Have you seen my script?