Using divs is a smart approach. One way to organize them is by implementing a floated layout with a wrapping div encapsulating the two right divs. Take a look at this example code snippet:
HTML
<div id="wrapper" class="clearfix">
<div id="sidebar"></div>
<div id="main_content">
<div id="top_right"></div>
<div id="bottom_right"></div>
</div>
</div>
CSS
#wrapper { background: #44BBF0; }
#sidebar { float: left; width: 100px; height: 500px; background: #485F40; }
#main_content { float: right; }
#top_right { width: 200px; height: 200px; background: #FF553F; }
#botom_right { width: 200px; height: 300px; background: #B0DE91; }
.clearfix:before,
.clearfix:after {
content: ".";
display: block;
height: 0;
overflow: hidden;
}
.clearfix:after {
clear: both;
}
.clearfix {
zoom: 1; /* IE < 8 */
}
You can visualize how it appears through this JS Fiddle link: http://jsfiddle.net/ddxYB/
Remember to clear the wrapper div to ensure proper alignment. As shown in the example, setting specific heights can be helpful, but automatic heights work just as effectively.
Take a glimpse at this screenshot from the JSFiddle code: