Chat BoxChatboxs can harm your forums in many ways they are a magnet for trolls and spam and also the forum itself may suffer due to lack of posts being made.
No one will join a site where all the talk is in the chat box they might as well go to yahoo chat. But if you still require one then please read on.
There are many free Chat boxes on the market just do a google search for free chat box.
There are some good and bad ones personally i would prefer to goto one that has a good support forum.
A list of the most used shoutboxes
There are of course a few more minor ones out there that offer little or no support at all, and some are even it would seem run by children.
What you have to remember is that some chat boxes do not like to be put in a forum description so it is best to add them to the forum footer read more on forum footer Here
Also you will have to allow html tags in your profile and forum config read more HERE Forum config and HERE Profile Settings