There is a simple Chat System that you can integrate into your VBULLETIN. It's called Flashchat and it only costs $5.00. Very Simple to integrate. I use it at my site.
I dont think this would be useful. As Trotter already said. Spammers would love this area. Would need constant attention by a Mod or Admin. We already have enough on our plate to get things done.
Wonder if getting a Vent server or a IRC channel would help..