The code details are not difficult using CSS (without javascript even). Go to any B&N and look at a book like "Eric Meyer on CSS" etc. for details on getting hover to change the DISPLAY vallue of the submenu anchors.
If you're serious about going beyond obsolete patchwork HTML and into standards-compliant dynamic CSS, you'll probably want to own (or at least study Meyer's book &/or:
Rachel Andrew's "CSS Anthology: 101 Essential Tips..."
Charles Wyke-Smith's "Stylin' with CSS: A Designer's Guide"
Pay full price at B&N... or get for 30% off at Amazon.