First some links:
This KB article should point you in the right direction with using the CDONTS stored procedure:
http://support.microsoft.com/default.aspx/kb/312839
You may also want to look into:
http://www.sqldev.net/xp/xpsmtp.htm
which is a much better alternative then CDONTS.
Now to answer your question about getting the email address into the 'To' field. Since you will, no doubt, have multiple birthdays on the same day, I would suggest selecting all of the days birthdays into a Temp table and then :shudder: use a cursor to loop through that table populating the to field with the current email address.
Your second question about personaliazation, inside the Cursor create 2 variables, one that is the message body and one that is the name of the user and do something like this:
Set @messageBody = @messageBody + ' ' + @userName
That should add the users name to the message for you.
hth.
"The one language all programmers understand is profanity."