The short answer is no. Each instant messaging network likes to use its own protocol, or at least keeps its own "group" in place and try to get you to bring your friends over to it. Its kind of a competition thing. The only exception I can see to this is AIM/ICQ, since they're both owned by the same folks now.
However, most of these IM apps have opened up their chat protocols so that third party tools could be written to access them. What this has done is opened the door to folks to create their own applications that aggregate all of these chat networks into a single hub for you to interact with. You typically dont't have the feature base that a single IM client provides, but you gain the benefit of being able to view them all simultaneously, without having to fire up multiple chat client apps at once.
You might look into an online application called Meebo, which would allow you to log in to your GTalk and your MSN Messenger at the same time. Its web based, so you can access it from nearly anywhere, and quite handy when you have multiple chat platforms that you want to keep dibs on.
Meebo also comes built in to another web app called threadsy, which is awesome if you're trying to collate your facebook/twitter/gmail type stuff too.