Adsens rectangle sidebar issue

Hey guys,

I am new at wordpress and am trying to add a rectangle image to my sidebar for 250 x 250 adsense. The theme that I have been modifying actually has two sidebars – both were set to 128px wide each. So I created a new div called sidebarad and added the sidebarad in my style sheet, making it 256 wide. the issue comes when I want to make it 256 height. It throws everything out of whack, putting my first sidebar1 to the left in the content area. Here is my style code:

#sidebarad {
background: transparent url(images/rectangle_bg.jpg) no-repeat top center;
border: none;
color: #443;
float: left;
margin: 0;
width: 256px;

height: 185px;

}

#sidebar {
background:#FFFFFF;

border: none;
color: #443;
float: left;
font-size: 11px;
margin: 0;
padding: 0 27px 30px 20px;
text-align: left;
width: 128px;
}

#sidebar2 {
background: transparent;
border: none;
color: #443;
float: right;
font-size: 11px;
margin: 0;
padding: 0 27px 30px 0px;
text-align: left;
width: 128px;
}

I added the sidebarad div above my sidebar div in the sidebar page. I’m going crazy here and sure would appreciate any help!