function CheckNumeric()
{
   // Get ASCII value of key that user pressed
   var key = window.event.keyCode;

   // Was key that was pressed a numeric character (0-9)?
   if (( key > 47 && key < 58) || (key ==13)){
      return; // if so, do nothing
      }
   else{
      window.event.returnValue = null; // otherwise, 
	                               // discard character
	  alert("Numeric characters only please");
	  }
}