mi dispiace, non so che dirti, non ho ne IE7 ne IE9 per fare prove.
ti posto intero il codice che mi funziona
codice:
<?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>
<meta http-equiv="Content-Type" content="application/xhtml+xml; charset=UTF-8" />
<style type="text/css">
*
{margin: 0; padding: 0; border: 0 none; outline: 0 none;}
body
{width: 100%; height: 100%; line-height: 1; font-size: 14px;}
.box
{text-align: left; width: 226px; height: 160px; float: left; position: relative; background: #fef6df; border: 1px solid #fdcb0a; margin-top: 6px;}
.box1
{text-align: left; width: 346px; height: 160px; float: left; position: relative; background: #fef6df; border:1px solid #fdcb0a; margin-bottom: 6px;}
hr
{width: 100%; height: 1px; background: #f00; border: 0 none; clear: both;}
</style>
</head>
<body>
<div class="box1">Testo1</div>
<div class="box1">Testo2</div>
<hr />
<div class="box">Testo1</div>
<div class="box">Testo2</div>
<div class="box">Testo3</div>
</body>
</html>