Variable substitution

Hi, I am trying to make an e-mail form so that I can generate an e-mail to send to all the users of the system. In the message part I want to be able to do something like this. Dear $fName, Welcome to ..... When it then sends the e-mail, it should substitute $fName with the current row in the database. For some reason it does not get automatically substituted when using mail(to, subject, message). Is there a function that substitutes variables with there values and returns a string. Any help is greatly appreciated, Thanks, Greg