Helping people with computers... one answer at a time.
There are a couple of programs that allow you to use more than one instant messaging service using only one client.
Macs have Fire, an instant messaging engine that captures in one place several different others (Yahoo, MSN, etc.). Is there something like that out there for PC users?
Well, there's good news and bad news. The good news is that there are definitely a couple of tools to do exactly what you want.
The bad news is that it might technically not be legal.
There are two popular packages that will do what you want:
Trillian, a commercial product for Windows with a free version that's been around for a long time, and has a large following.
Pidgin is an open source client that runs on several platforms.
Both are compatible with the major instant messaging clients like AIM, MSN Instant Messenger, Yahoo, ICQ and others.
And therein lies the controversy.
Instant messaging protocols are typically closed. The protocols used by MSN Instant Messenger, or AOL Instant Messenger are not public protocols. Tools like Fire, Trillian, and Pidgin have all had to reverse engineer the protocols to work. And if the protocol changes, the tools break until the tools are updated to be compatible.
And, technically, using a non-supported client such as Trillian or Pidgin is probably illegal. From AOL's point of view, for example, users of those programs are depriving them of the ability to display the advertising that supports the free service.
I wish that the services could agree on a common protocol or a way of interoperating or at least supporting a common client. But they do not.