Link 2 MySQL databases

I currently have 2 MySQL databasis. I purchased a script for keeping track of links clicked in emails. This script does not have a signup and login section. I have added a signup and login MySQL database to MySQL_Admin, and now need to have the two databasis linked, as the link tracking script still stores all user data regardless of who I log in as. I have completed the PHP portions of the databases and only need the databases linked so that each users info is stored seperately. I will forward my domain details for you to have a look at the databases, once you need the information.