aMSN and Kopete should be able to do IM+video, if the protocol being used supports it (though aMSN is horrible, and works for Messenger only, so you don't necessarily want that). Not sure about audio, though. Doesn't Skype, or one of it's "clones" for Gnome, do text chatting too?
EDIT: might want to check this out:
http://telepathy.freedesktop.org/wiki/