A very nice bit of regex here to validate an emailaddress

function isEmail($email){
 if(eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $email)) {
   return true;
 }else{
  return false;
 }
}