If statement to define options in listbox

Hi

I'm trying to make a listbox where the options are dependent on another variable in my worksheet. If my variable n.sec is smaller than 3, I want the list box to only have the option "N/A". Otherwise I would like it to display a list of options.

I'm having a hard time understanding the vb script language, and haven't been able to find a simple tutorial to get me started in using it in mathcad. I hope someone can give a solution to my problem, which I believe must be pretty simple, but I just can't crack.

Thanks in advance

Ole