How To - Use Info

[Preech]

Okay, here is my question.
I have vbulletin installed, everything works fine. I am still in the process of building everything else within vbulletin, from some other purchased third party scripts. I already know how to create a new template, so that the pages from the other script will be rendered using vbulletins styles. How do I go about implementing vbulletins login system, to work with that third party's script, instead of using the third partys login.

I wish to do this, because this script does not have a usergroup permission system like vbulletin does.
If you wish to know what the third party script is, please send me a PM, and I will glad give you that information, if you are able to help.