使用showModelessDialog打开的窗体如何在动态改变窗体的大小

<HEAD>
<HTML>
<HEAD>
<TITLE>showModelessDialogEX.htm</TITLE>
<SCRIPT>
var sUserName="";
function fnCallDialog()
{
showModelessDialog("myDialog.htm",window,"status:false;dialogWidth:300px;dialogHeight:300px");
}
function fnUpdate()
{
oName.innerText = sUserName;
}
</SCRIPT>
</HEAD>
<BODY>
<P>Enter your first name: <SPAN ID="oName"
STYLE="color:red;font-size:24">Joan</SPAN></P> <INPUT TYPE="button"
VALUE="Display Modeless Dialog" onclick="fnCallDialog()">
</BODY>
</HTML>