I would think these forums are using JavaScript is it wouldnt be as easy as using their code. Here is a guide to see
how its done via JavaScript.
You might want to consider using HTML & CSS as it probably would be easier. See the
HTML Guide.
If you want a quick an easy option you can use this
on-line tool to create the menu for you. I haven't tried that tool before so I don't know how good it is.