I wouldn't think you need to do anything special for drupal but I could be wrong abut that.
I would suggest that you just use a typical suckerfish dropdown, it would just need a script for li:hover in IE6 as always.
Here are some examples you can look through if you are not sure how to get started.
You would just need to set up some classes so you can target each LI with a specific image. You will find just about every variation of menus in that second link.
I would encourage you to set up an image replacement technique though so your menu still makes sense if the viewer has images disabled.