There are pros and cons to the IM window on the pages of the forum. Forum administrators often have to weigh the pros and cons of forum functions and features.
Padre also has a point, when the window is on the forum, it can appear that one is either chatting or surfing the internet all day, could save some trouble for some TeaChatters at work. With only TeaChat and no IM open, some of this is minimized.
I simply open a seperate tab for IM. This will allow the screen to go beyond the normal 2 hours of IMs. As long as the window is open and not refreshed, I can have a whole day's worth of IMs.
For TeaChat, it is common for me to have several tabs open. One for the general forum, one for TeaDay, one for IM, one or more for hot topics I am watching, and one for admin function (moderator functions).