Probably the most efficient and easiest way in the long run would to create your site based around vBulletin code. Using their user system (if you redirect your "register.php" to vBulletin's, it will handle most of that) you could easily have cookies log you in to both places. Also, you can use "Custom Profile Fields" for certain data and import them into those (I forget how they are stored tho...)

Absolutely no argument here. We just have different approaches. Rather than starting out saying "that's the wrong way", I tend to answer the question being asked, then start pointing out that there might be a different and better approach.

Obviously the best approach is as you suggested. Use the usual mechanisms for including vB in external apps, and drive the portal site off of vB's authentication and registration.

-- hugh