If you are chatting with your friends instead of working, then your boss has
reason to complain. If you continue chatting even when you have been told
not to, and attempt to hide the fact by using alternative software for the
purpose, you will have no reason to complain if you are fired. If you don't
like the rules, get another job where the rules are different.

And no, there isn't a way to get Yahoo messenger to work inside Office, at
least not without the programming you don't know how to do.