If I understand you correctly, you want a vertical menu? Just any vertical menu, or a vertical MAIN MENU ?
my TT theme has a horizontal MainMenu, and a series of vertical menus which act like submenus, depending on which MainMenu item you have clicked on.
For this to work, its mostly joomla configuration.
First, I styled the module in the left position the way i wanted it. In the CSS the styling prefix is " ttr_vmenu "
I then added a normal Menu module to the LEFT position, and configured the settings for the menu to use the prefix of _vmenu.
Then, from the MenuManager, I went to my menu, and started adding single_article links, and iframes, and other modules and plug-ins as desired ... normal joomla stuff at this point.
I set the permissions so that it would appear on NONE of the pages except those selected (as appropriate), and bingo! I had functional vertical menus INSIDE the MainMenu items. I even have SubMenuItems (flying out) from the vMenus.
This is totally doable.