User integration with web application

[travisp]

(Note: I was redirected from vbulletin.com and so some content may be similar)

I've seen a few posts about similar things, but most seem to be about existing third party applications (e.g. wordpress, joomla).

Basically, I'm developing a PHP web application that I want to have an accompanying message board and I want to integrate my user accounts with the message board such that:

1. Users don't have to create separate user accounts -- their account for my website will create the vBulletin account.
2. Users don't have to login separately to vBulletin -- if they login to my website, they should get logged into the vBulletin forum.

I want to do this for a few reasons, but the main one is to encourage forum participation by making it easier for users of the website to jump right into the forums if they wish.

How difficult is it to do this integration with the latest version of vBulletin (some of the mods I found by browsing this site were for older version of vBulletin)? Are there any problems with doing this that I should be aware of?