Prova così:
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
	<head>
		<title>Documento senza titolo</title>
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
		<style type="text/css">
.div-1 {
	border: none;
	height: 400px;
	position: relative;
	text-align: left;
	width: 400px;
}

.div-1-1 {
	border: #000000 solid 1px;
	border-right: none;
	height: 400px;
	left: 0px;
	line-height: 400px;
	padding: 0px;
	position: absolute;
	text-align: center;
	top: 0px;
	width: 200px;
}

.div-1-2 {
	border: #000000 solid 1px;
	height: 400px;
	left: 200px;
	line-height: 400px;
	padding: 0px;
	position: absolute;
	text-align: center;
	top: 0px;
	width: 200px;
}
</style>
	</head>
	<body>
		<div class="div-1">
			<div class="div-1-1"></div>
			<div class="div-1-2"></div>
		</div>
	</body>
</html