Your problem is indeed the CSS, if you do not already use it I would recommend using FireBug which is a very good debugging addon for FireFox.
Also, maps are (in my opinion) rather useless. It is usually a better idea to use images on a layer on top of the base image.
To fix the CSS problem you need to change the margin of the header. There are probably better ways to do this, but I played about for a few minutes in firebug and found that setting the padding and margin to 0 only worked for half of it. This way does work:
#header {
height:113px;
margin-top:-55px;
}
I hope it helps.
~Shane Hudson