How could I create a cascading selection in NS without applets and Activex ? ie:

Categories
----------
Beverages
Fruits
Deserts
...

*Selecting fruits would show :
Orange
Banana
....

I can do this treeview like in IE but not in NS (with and w/o XML-XSL). In IE I can also add, remove options on the client-side but in NS I can't do that even playing with styles. I would appreciate any help with some sample if possible. TIA.
Cetin