Add php functions to existing script to perform database upd

My project involves writing and adding php functions that update a Mysql database to an existing website script. The scripts involved are Boonex Dolphin and phpProbid. I have both scripts installed on a single website and both scripts share the same database. The Dolphin site allows members to purchase an upgrade to a new membership level. When this upgrade is purchased, I would like to have the user's Dolphin username and password added to the phpProbid member table. In other words, when the member of my Dolphin site upgrades their membership, login credentials/an account is automatically created for them so that they can login to the phpprobid site. I have figured out how to automatically add a user to phpprobid when they register at my Dolphin site, however, I am stuck on where exactly to put the code so that they aren't added to phpProbid until they pay the upgrade fee. I will be happy to share what I have put together with the freelancer which should save them some time in finding which database tables need to be considered, which file does the upgrade to the database when the IPN indicates successful payment, etc. I have fresh installs of both scripts running and can provide the freelancer with access to ftp, Mysqladmin, and administrative control panels to develop/test their work. What I would like in the end: -User is registered automatically in phpProbid after paying for membership upgrade in Dolphin -If a member uses the "change password" function in Dolphin, it will also update their password in the phpProbid user table - When Dolphin upgrade time expires, the function already in Dolphin that automatically downgrades the member's membership will also change the member's active/suspend setting in the phpProbid table to "suspend".