Previous post not solve your problem.
Here is a suggestion.
I assume that you want to send birthday message to all member whose birthdate stored in database in time stamp format this time stamp format must be php $date=time(); during registration or posting of birth date.
This script will help you to send the birthday message to all member has the birthday.
$query=mysql_query("select name from people where birthday > $from and birthday <= $to");
mail for every person
You can run this script through cron jobs so that it will automaticaly execute on a particular time. you can change this code according to you convenience