If you are using the DDR Menu ... and you should be ... then you might want to start with the ULTokens template. That will render the menu as an unordered list. You can style this with CSS to create a vertical list. Look at some of the other templates to see how the templates, CSS and jQuery are used together to create a variety of menus.
Look particularly at Andy's recent tutorials on skinning, as these include discussion and demos of customizing menus. Last months tutorial on creating XSLT templates (
http://www.dnncreative.com/Tutorial...ault.aspx) will be specially useful.
The basic set of teimplates includes a treeview template that might prove helpful