Well have a look here:
vBulletin 3.7 Add-ons and try to find what you want, if you can post a link to it here.
then we can continue this thread because this'll go nowhere the way it's going now.
I noticed it's a module on the left hand side as part of
vBadvanced
It's located above 'Todays Birthdays' for logged in users at
www.althanas.com
Look at the online users module. It works much like that.
Though it gives you an option to directly PM them, look at their profile or remove them from your friends list. - They also only appear on the block if they are online.
I can't see why it wouldn't already be built into VB 3.7 and just activatable, it'd join all the other module blocks at the bottom of the main page I imagine.