My knowledge about chat software is zero. Vbulletin out of the box does not have this capability.
Also, from what I have read so far, I think PHP/MySQL doesn't work well for on-demand chat. It seems you have to run any chat applications on your own server, and the sheltie forums, like most forums, runs on shared servers. (At this time, a dedicated server is way outside of this forum's budget.)
Since I have no experience with this type of add on, I have posed the question to my hosting company for their opinions & suggestions.
If there is a solution (& it is reasonably priced & doesn't require a dedicated server), I would certainly be willing to implement it.