This menu is an adaption of Dynamic Drive's Glossy Vertical Menu. The modifications have been to simply add a sub menu on certain links and to add styling to the menu boxes by rounding the corners. This has simply been done using classes to add fixed width images to the top and bottom. See below:
sub_top.gif
You'll obviously see that when you hover over certain links, the submenu box isn't the same styling as the main menu. I figured i'd keep it this way so that you can see how by the sub menu works - the top link in the sub menu a class called subtop and the bottom link in the sub menu uses a class called sub_bottom. If you don't need the extra styling in your sub menu the just take out those 2 classes.
Again like other menus i've altered, it simply mixes the regular menu with DD's Drop down tab menus
horizontal menu with rounded corners
horizontal menu with rounded corners and a drop down
Hope it helps,
Kujee