Here's a before and after picture. When I add a float:left to the li, the layout breaks and the div that's supposed to be below this topmenu div, floats up.

Here's the CSS:
#topmenu
{
background-color:#335D7C;
}
#topmenu ul
{
list-style:none;
margin:0;
padding:0;
}
#topmenu ul li
{
background-image: url('../Content/Images/topmenutick.png');
background-repeat:no-repeat;
color:White;
float:left;
padding-left:15px;
padding-right:15px;
}
#topmenu ul li a
{
text-decoration:none;
}
#topmenu ul li a:hover
{
text-decoration:none;
}
clear: both;to whatever element is supposed to be below the floated list.