Simple two column html layout without using tables

<style type="text/css">
#wrap {
   width:600px;
   margin:0 auto;
}
#left_col {
   float:left;
   width:300px;
}
#right_col {
   float:right;
   width:300px;
}
</style>

<div id="wrap">
    <div id="left_col">
        ...
    </div>
    <div id="right_col">
        ...
    </div>
</div>

Make sure that the sum of the colum-widths equals the wrap width. Alternatively you can use percentage values for the width as well.

For more info on basic layout techniques using CSS have a look at this tutorial