hooking in the login/registration process
 

I am wanting to use the user/member database from vbulletin to control access to my site as well. First of all i need to hook the login system so when they login into my main site, they get logged into the forum system as well and stay logged into the forum weatre they are browsing my main site of the forums. I also need to hook the registration process so when they register on my site they automatically get registered with the forum system too. I also need to use the user groups from the forum system from my site to limit link so admins can see teh links that regular user can't. any help on where to look, what files i need to look at, etc.. would be great.

Thanks

Anyone? I rather not just go looking into the code blinding but looks like i might have too