Twenty Eleven – Menu Hover – Show All Menu Items

I want to change the Menu Hover option in Twenty Eleven.

When I hover over the a Menu option I would like to see all of the Menu Options for all parent pages and all their children. There will only be two levels.

There is an example of what I am trying to achieve at http://www.ul.ie (University of Limerick).

I have spent ages trawling the internet and no assistance any where so far.

Regards

Brendan