What is happening...
The site uses the <div> tag to create the layout.It uses a fixed area at the top of the page for the menu. The lower portion is then split into two separate areas or a single area depending on the page you are viewing.
The menu that I am using can be found here with an excellent explanation of how the different parts of the code work.
Feel free to have a browse. If things are not quite right then bear with me and hopefully it will all be working soon.
Have a look here for another site I have created