loading the page do wait?

<INPUT class=MyButton name=AddVal onclick=Javascript:OnAddVal() type=button value="Address Validation"  style="width: 114; height: 21" tabindex="404">

function OnAddVal()
{
        if (confirm("Are you sure you want to perform Address Validation?"))
              {
            window.showModalDialog("XMLValidator.aspx?ValType=AddVal&AppNo="+document.getElementById('AppNo').value+"","","height=400,width=500,toolbar=0,menubar=0,scrollbars=1,resizable=1");
              }
        else
        {        }
}