Writing custom registration pages

[sqook]

Hi,
I was directed to this forum by vBulletin support, and am wondering if it is possible to write a custom registration system for this forum software. Basically, we are looking for a way to create a public support forum, but to limit access to users who have already registered their products on our website (which is powered by a mysql database). Non-registered users would of course be able to read the site, but not create accounts or post. The goal here is to basically create a plugin where users wanting to sign up for the forum would simply enter their product serial number and their registration would be confirmed through some type of script which would connect to our database.

Is this possible to do? And if so, where could I find documentation detailing how I might go about such a task?

Thanks!