Greetings John,
Using Windows Live Messenger, you can communicate to Yahoo Messenger contacts, but that's
about it I'm afraid.
Using Windows Messenger and connecting to the normal public .NET Messenger network, you can
only talk to those there.
Other products are available that allow logging into multiple instant messaging networks at
the same time, like Pidgin, Trillian and others, but you'll need an account on each network
and their support for each network is usually rather limited. For instance Pidgin doesn't
correctly send font information to [.NET] Messenger contacts nor does it do file transfer
very well.
--
Jonathan Kay
Microsoft MVP - Windows Live Messenger
MSN Messenger/Windows Messenger
MessengerGeek Blog:
http://www.messengergeek.com
Messenger Resources:
http://messenger.jonathankay.com
(c) 2008 Jonathan Kay - If redistributing, you must include this signature or citation