I played around with your CSS.
You could try replacing these two sections:
ul#navbar {
display: inline;
list-style-type: none;
padding: 0.3em;
margin: 0.3em;
top: 1em;
left: 12em;
}
ul#navbar li {
float:left;
margin: 0.5em;
padding: 0.3em;
border-right: none;}
Now you need to add a 'clear' in your HTML-Code too:
<div class="header"
style="clear:both"><img src="images/MMMheader.bmp" class="head"/></div>
Note: You'll get larger (vertical) spaces between the menu links now. Maybe changing the margins/paddings will help. It's too late, i can't look into it now.