Create a user account system

I’m having a heck of a time trying to find out how to create an online user account system. You know, register at ebaumsworld.com and you can comment on posted items and post in the forums? How do you go about creating a system like that? I’m wanting to build a pretty robust website using wordpress and allow users to login so they can contribute to the forums (possibly vBulletin) and sign up for the email list. How do I go about creating such a thing? Does this fall under the category of database also? Thanks for any help.