portrait = false 即为横向.

<object id="factory" style="display:none" viewastext classid="clsid:1663ed61-23eb-11d2-b92f-008048fdd814"
codebase="http://www.meadroid.com/scriptx/ScriptX.cab#Version=5,60,0,360"></object>
<script defer>
function window.onload() {
  factory.printing.header = "（自定义页眉）"
  factory.printing.footer = "（自定义页脚）"
  factory.printing.leftMargin = 0.75
  factory.printing.topMargin = 1.5
  factory.printing.rightMargin = 0.75
  factory.printing.bottomMargin = 1.5
  factory.printing.portrait = false    // 横向打印
  }
</script>

<p><input  type="button" value="打印本页"
 onclick="factory.printing.Print(false)">
 <input  type="button" value="页面设置"
 onclick="factory.printing.PageSetup()">
 <input type="button" value="打印预览"
 onclick="factory.printing.Preview()">
<br>
<a href="http://www.meadroid.com/scriptx/docs/printdoc.htm?static" target=_blank>具体使用手册，更多信息，点这里</a>