It appears that specifying the <div> height as a percentage breaks the version 6 map control. Here's a simple example:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script type="text/javascript" src="http://dev.virtualearth.net/mapcontrol/mapcontrol.ashx v=6"></script>
<script type="text/javascript">
var map=null;
function GetMap()
{
map = new VEMap('myMap');
map.LoadMap(new VELatLong(34.0540, -118.2370), 14, VEMapStyle.Road, false, VEMapMode.Mode2D, true, 1);
}
</script>
</head>
<body onload="GetMap();">
<div id='myMap' style="position:relative; width:100%; height:100%;"></div>
</body>
</html>
Above code renders a blank page in IE6. Changing the <div> height to, say, 400px works. Any ideas