Sync AD user credentials with a SQL database

Hi folks!

I need some help to how Sync the user and password from my Active Directory, to a SQL Database.

Actualy, my enviroment have a database with users and password added, my custom applications uses it like a passport, but now I want to use Active Directory to control these users, but I can't use windows authentication in my old apps. I was reading about Forefront Identity Manager to do this, but I need a free solution.
The Sharepoint database sync user credentials with AD? Any ideas how I can do this?

Thanks in advance!

MCTS Exchange 2010. @pedrongjr