First off, don't double post. We don't like it.
What database system are you using?
All you'd need would be a simple script running sending an SQL statement to the database, asking to retrive the dates birthdays..
Something along the lines of
Code:
SELECT name FROM users WHERE birthday = date;
which will return a list of all the people in the database who's birthday is today...
The script/php will have to supply the date in the same format that you've saved the birthdays...