What about this:
<!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">
<head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /><title>
test
</title>
<!--[if lt IE 8]>
<![endif]-->
<!--[if lt IE 7]>
<![endif]-->
</head>
<body style="margin: 10px;">
<div id="wrapper" style="width: 960px; margin: 0 auto; position: relative; border: 1px solid red; overflow: hidden;">
<div id="header" style="float: left; width: 185px; height: 600px; top: 10px; border: 1px solid blue;">
header
</div>
<div id="content" style="width: 650px; float: left; background: white; left: 185px; min-height: 600px; height: 600px; border: 1px solid lime;">
content
</div>
<div id="rightcolumn" style="float: left; top: 10px; width: 90px; left: 865px; height: 600px;border: 1px solid maroon;">
right
</div>
</div>
</body>
</html>
It works on IE7, Firefox, Opera, Safari and Chrome. I guess it will work in IE6 and IE8 too. I had to reduce the width of the "content" because the (rightcolumn+content+header) < wrapper