The easiest way to do this is to just fake it. A List Apart has covered this extensively over the years, like in this article from Dan Cederholm from 2004.
Here's how I usually do it:
<div id="container" class="clearfix" style="margin:0 auto;width:950px;background:white url(SOME_REPEATING_PATTERN.png) scroll repeat-y center top;">
<div id="navigation" style="float:left;width:190px;padding-right:10px;">
<!-- Navigation -->
</div>
<div id="content" style="float:left;width:750px;">
<!-- Content -->
</div>
</div>
You can easily add a header onto this design by wrapping #container in another div, embedding the header div as #container's sibling, and moving the margin and width styles to the parent container. Also, the CSS should be moved into a separate file and not kept inline, etc. etc. Finally, the clearfix class can be found on positioniseverything.