Border around Header in Boxed layout

Hi, the fluid layout didn't work out as my friends said in some of their browsers the whole header did not show. They had to scroll over to see it. So I switched to the boxed layout. The border color around it does not work for my header well. I would like to remove the entire border with the exception of a thin line below the menu to separate it from the post page. Also, I would need to extend my header image and menu to fit properly over the content. Can you guide me? Thank you, Nancy