The key is CSS plus a touch of Javascript. I find this <a href="http://www.alistapart.com/articles/horizdropdowns/">How-to</a> quite complete and it explains step by step what to do and change to first make the menu then make it work with IE (and it does, tested with IE the "prettier one"). Also see <a href="http://www.alistapart.com/articles/dropdowns/">this one</a>.