I have the same problem.
I think it's possibly a cookie problem with me because I have the portal setup at http://www.domain.com and the VB at http://forums.domain.com.
Any ideas or help would be appreciated.
Well, I take back what I said about the cookies. Just found the option to allow the entire site to use the cookies and that didn't fix it.
The Online function of vBindex does not always record people as being online straight away - You may have to refresh the page to get the entire list of online people - This is known by us, and we shall try and sort this out for a future release...
As for the login problem, you may have to edit the vbindex_navbar template, and change the url of the login form to reflect the location of your forum's login.php file...
If this is not the problem, or does not fix it, could you reply again and I'll try and think of another way of sorting it :)