Category Menu help?

Ok my question is i would like to make a category menu… Basically i would like it to have a couple buttons for the Parent categories and then when u hit one a list appears below of all the Sub cats.

This site has what im lookin for…click here
Just click any of the big buttons and you will see…

Sorry i cant give a link for my site because its only runnin on a local server.. Thanks for any input