Java applet visible through pop-up menus

I've created a pop-up menu, which pops up over a java applet on the page. The
problem is, the java applet appears on top of the menu, although the menu
should be on top of the applet (if you see what I mean). I've also noticed that
this problem occurs with certain types of form field, such as drop-down menus.
Does anyone have a solution to this?

Thanks!