DIV Positioning Without Using Absolute?

[URL]
<style>
div#back{
width:1000px;
height:1000px;
margin-left: auto;
margin-right: auto;
background-color:#096;
}div#topmenu{
width:400px;
height:35px;
position:relative;
top:5px;
left:595px;
background-color:#9F0;
}div#logopart{
width:950px;
height:70px;
position:relative;
top:0px;
left:50px;
background-color:#0FF;
}div#leftmenu{
width:100px;
height:400px;
position:relative;
top:0px;
left:0px;
background-color:#999;
}div#cont{
width:900px;
height:500px;
position:relative;
top:0px;
left:0px;
background-color:#FF6;
}</style>...
<div id=back>
<div id="topmenu">topmenu</div>
<div id="logopart">logopart</div>
<div style='display:inline;'>
<div id="leftmenu">leftmenu</div>
<div id="cont">cont</div>
</div></div>

How do I put "cont" div on the right of "leftmenu" without using "absolute"?? The screenshot was little bit cropped out and there is no problem on width.