Hi everyone i have got a bit of an issue with this

In dreamweaver it looks like this ^^

But in IE it looks like this

Does anyone know whats goin on here, I mean it all looks ok at the end but in design view its not right.

.leftside {
background-color: #CCCCCC;
display: block;
width: 20%;
border-bottom-width: 1px;
border-bottom-style: solid;
border-bottom-color: #333333;
font-family: Arial, Helvetica, sans-serif;
font-size: 11px;
border-right-width: 1px;
border-right-style: solid;
border-right-color: #999999;
position: relative;
float: left;
margin: 0px;
padding: 0px 0px 0px 10px;
}
.Header {
font-family: Arial, Helvetica, sans-serif;
width: 100%;
}
.contentmid {
font-family: Arial, Helvetica, sans-serif;
background-color: #dee8f1;
width: 59%;
border-left-style: solid;
border-left-color: #FFFFFF;
float: left;
position: relative;
border-left-width: 1px;
border-bottom-style: solid;
border-bottom-color: #666666;
border-bottom-width: 1px;
font-size: 11px;
display: block;
margin: 0px;
padding: 0px;
border-right-width: 1px;
border-right-style: solid;
border-right-color: #FFFFFF;
}
.right {
font-family: Arial, Helvetica, sans-serif;
font-size: 11px;
background-color: #8DA7C2;
display: block;
border-bottom-width: 1px;
border-bottom-style: solid;
border-bottom-color: #666666;
margin: 0px;
padding: 0px 0px 0px 5px;
float: right;
clear: left;
width: 20%;
left: 75%;
border-left-width: 1px;
border-left-style: solid;
border-left-color: #5C83A9;
}


Please help
oh.. and I'm a total NOOB at css