While an online Chat system might be interesting, I don't think that it would really benifit too many people for the headache it might be to get it running.
On the whole, I rarely see more than 1 or 2 people logged in at one time. It would be much easier to use dedicated software for that purpose, which most of us already have, "Skype". I'm sure that you have heard of it,
If not here is the link:
http://www.skype.comThe basic package is free and should suffice for file transfers, text, voice and video communication
I also think that there may be a Skype Directory thread somewhere on this forum, if not check user profiles, if a member has a Skype account they most likely have it posted in their profile
My Skype name is, thumper7458 (no surprise there) you can add me if you like.