I have a Windows Live ID and I use it to talk with my friends, who use Windows Live Messenger 2009 or 2011. I've adopted Pidgin as my main conversation client because it is universal and it is cross-platform.
However I still can't have video conversations with my contacts, the options are all grey and I can't configure anything.
How do I configure pidgin to be able to make video and audio conversations with Windows Live Messenger users? Is there any missing plugin?
You can't really, for the simple reason that it's not correctly implemented for now.
From Pidgin's FAQ:
More documentation can be found here with current progress on video chat support in Pidgin.
Well, You can try third-party plugin from:
http://developer.pidgin.im/wiki/ThirdPartyPlugins
msn-xmpp - but i think it will not work(although You should try)