296729 GeekLog Integration

I am creating a website that is a hybrid of an online matchmaker (dating) service. The core software is already created (it is written in PHP). Members can search other user profiles for a match, chat, message, etc. I would like to integrate Geeklog (also written in PHP) as an extension to the matchmaker program. So, when a new user registers on the matchmaker site, they are also registered on Geeklog. And, when they login to the Matchmaker site, they are automatically logged in to GeekLog. Both the matchmaker script and GeekLog have their own mysql database. When a user registers for the first time in matchmaker, I would like the GeekLog database to be updated with the user id/password info. And, when the user "moves" from the matchmaker script to the GeekLog script, I do not want them to be required to log in again to GeekLog. I know enough php to be dangerous, and can make geeklog look like the matchmaker site. Therefore I will handle the design. But I am looking for assistance in integrating the above registration and authentication, so that when a user goes to one program to another it is seamless.