function isZip(sText)
{
	var ValidChars = "0123456789-";
	var IsNumber=true;
	var Char;
	for (i = 0; i < sText.length && IsNumber == true; i++) 
	   { 
	   Char = sText.charAt(i); 
	   if (ValidChars.indexOf(Char) == -1) 
	      {
	      IsNumber = false;
	      }
	   }
	return IsNumber;
}