父窗体：<script language="javascript">
function openwin(rid){
var srcFile="UserUpdate.aspx?type=UserUpdate&id="+rid; varwinFeatures="dialogWidth=600px;dialogHeight=600px;scroll=no;resizable=yes;help=no;status=no";
var obj=form1;
window.showModalDialog( srcFile,obj,winFeatures);
}
</script>

子窗体：

function send(val){
var myobj=window.dialogArguments;//showModalDialog传递参数得用这个
myobj.parent.value=val;
window.close();}

<input type="button" value="确定" onclick="send(form2.zi.value)">//zi是子窗体传值控件的id