For whatever reason I've never liked the clearing approaches, I rely on floats and percentage widths for things like this.
Here's something that works in simple cases:
#content {
overflow:auto;
width: 600px;
background: gray;
}
#left, #right {
width: 40%;
margin:5px;
padding: 1em;
background: white;
}
#left { float:left; }
#right { float:right; }
If you put some content in you'll see that it works:
<div id="content">
<div id="left">
<div id="object1">some stuff</div>
<div id="object2">some more stuff</div>
</div>
<div id="right">
<div id="object3">unas cosas</div>
<div id="object4">mas cosas para ti</div>
</div>
</div>
You can see it here: http://cssdesk.com/d64uy