How to Build This Menu
The structure closely follows the original from A List Apart, including the Javascript.
The styles have been heavily annotated to help me (& you) figure out exactly how they work. Along the way, I ran into an IE bug that prompted me to build this horizontal white gap dropdown menu bug page, and another one that led to this bug demo Disappearing Dropdown Bug
Minor changes to the Javascript were made Feb 22/09 to pass XHTML 1.1 Validation (CDATA comments were added)