function OpenWindowWithPost(url, windowoption, name, params)
   {
            var form = document.createElement("form");
            form.setAttribute("method", "post");
            form.setAttribute("action", url);
            form.setAttribute("target", name);

            for (var i in params) {
                if (params.hasOwnProperty(i)) {
                    var input = document.createElement('input');
                    input.type = 'hidden';
                    input.name = i;
                    input.value = params[i];
                    form.appendChild(input);
                }
            }

            document.body.appendChild(form);

            //note I am using a post.htm page since I did not want to make double request to the page
           //it might have some Page_Load call which might screw things up.
            window.open("post.htm", name, windowoption);

            form.submit();

            document.body.removeChild(form);
    }

   function NewFile()
   {
       var param = { 'uid' : '1234'};
      OpenWindowWithPost("NewFile.aspx",
      "width=730,height=345,left=100,top=100,resizable=yes,scrollbars=yes",
      "NewFile", param);
    }