Here are some tutorials on the net about how to create various menus

Horizontal Top Nav Menu

• Sliding Door Technique for horizontal tabs by Douglas Bowman who gave this excellent talk on CSS techniques.
• Graphical Horizontal Menu - with hover effect using unordered list

Vertical Side Menu

• Taming an Unordered List to create Vertical menu. To avoid using tables for menus, you typically use unordered lists.
• Uberlink CSS List Menu - includes hover effect and highlight selection. It uses the Uberlink javascript script to highlight the selected menu based on the URL.

Drop Down Menus

• Digg-style Drop Down menu - uses ul and li's in conjunction with Javascript