function validateZIP(field) {
var valid = "0123456789";
if (field.length!=5) {
alert("Please enter a 5 digit Zip code.");
return false;
}
for (var i=0; i < field.length; i++) {
temp = "" + field.substring(i, i+1);
if (valid.indexOf(temp) == "-1") {
alert("Invalid characters in your zip code.  Please try again.");
return false;
}
}
return true;
}