one of the problems with this is that when the words do wrap, it cannot dynamicly set the hight of the container.
This means that you need to set the height of the menu items to something like 30px to allow for the second line. the height needs to be set to give the line a place to wrap to, other =wise, the line will wrap, but it wont be seen, because it will fall outside of the container available to the link text.
then in the css you can add a white-space: normal; setting to wrap the text.