Using general CSS/(X)HTML:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title></title>
<link rel="stylesheet" type="text/css" href="css/stylesheet.css" />
<style type="text/css" media="all">
#wrapper {width: 100%; position: relative; }
#header {width: 100%;text-align: center; }
#left-col {width: 24%; display: inline-block;}
#main-col {width: 48%; margin: 0 1%; display: inline-block;}
#right-col {width: 24%; display: inline-block;}
#footer {width: 100%; clear: both; text-align: center; }
</style>
</head>
<body>
<div id="wrapper">
<div id="header">
<h1>...header-content...</h1>
</div>
<div id="left-col">
...left-col content...
</div>
<div id="main-col">
...main-col content...
</div>
<div id="right-col">
...right-col content...
</div>
<div id="footer">
...footer content...
</div>
</div>
</body>
</html>
<div id="wrapper">
<div id="header">
...content...
</div>
<div id="left-col">
...content...
</div>
<div id="main-col">
...content...
</div>
<div id="right-col">
...content...
</div>
</div>
This works, but it isn't particularly pretty, and you're still left to deal with the column heights and locations yourself.