function validate(field) {
var valid = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789.,- "
var ok = "yes";
var temp;
for (var i=0; i<field.value.length; i++) {
temp = "" + field.value.substring(i, i+1);
if (valid.indexOf(temp) == "-1") ok = "no";
}
if (ok == "no") {
alert("Invalid entry. We apologise for the inconveneince, but to prevent spam, this form only allows alphabetical letters and numbers.");
field.focus();
field.select();
   }
}