一个菜单用window.createPopup();实现的问题?

<script language="JavaScript">
PopMenu = window.createPopup();
function showSelect()
{ window.location.href="a.htm";
}
function showPopMenu()
{
w=100
h=100
var str = "<table id=mypopup border=0 cellpadding=2 cellspacing=0 width=200 height=100 style='background: #89CB10' >";
str += "<tr><td id='aaa' >-----</td></tr>";
str += "</table>";
PopMenu.document.body.innerHTML = str;
PopMenu.document.all.aaa.attachEvent("onclick",showSelect);
PopMenu.show(100, 148, w, h,document.body);
}
function hidePopMenu()
{
PopMenu.hide()
}
showPopMenu();
</script>
<html><head></head><body></body></html>