function USPS_Window(){
	window.open("http://www.usps.com/zip4/","USPS_Zip_Win","height=440,width=675,toolbar=no,scrollbars=yes,resizable");
}

function checkZIP(txtZIP){
  var theEntry = "";
  theEntry = txtZIP.value
  illegalEntry = "Your zip code entry, \"" + theEntry + "\", is not valid. Please try again, using the format \"12345-1234\"."
  if ((theEntry == null) || (theEntry.length == 0)){
  	window.alert("Please enter a zip code with its four digit extension.");
    txtZIP.focus();
    return false;
  }
   else if (theEntry.length < 10){
   	window.alert(illegalEntry);
    txtZIP.focus();
   	txtZIP.select();
    return false;
  }
   else if (!isZIPCode(theEntry)){
   	window.alert(illegalEntry);
   	txtZIP.focus();
    txtZIP.select();
    return false;
  }
   else{
   	return true;
   }
}