How does vBulletin detect when someone enters the forum?
 

When someone enters the forum, the guest count is increased. How is this done? Is it done through the session code? And if so, where is the session code located?

Yes, it's the session code. And, code concerning sessions can ultimately be traced to class_core.php I believe. (I may be wrong on that one - relying on memory)

Thanks amy! I'm trying to create a session on a page outside of the vbulletin directory. How would I do this? I assume the current session code is accessed in the common vBulletin header but I haven't been able to find it.