Show/Hide Layers from a drop down box

Dear people,

I need to show and hide several layers each time an item is selected. For example if my select box contains 2 items; “north” and “south”, when “north” is selected I want to show layers “mapnorth”, “dirnorth” and “optnorth” whilst hiding “mapsouth”, “dirsouth” and “optsouth” and vice-versa when “south” is selected.

Is this possible? If so, can someone tell me how to do it?

thanks
m