Post from Lync Team explaining how to configure Lync Group Chat as preferred IM client when Lync Group Chat and Lync are installed.
Read more at source: http://blogs.technet.com/b/nexthop/archive/2011/07/19/how-to-make-lync-group-chat-client-the-preferred-im-client.aspx
Cheers,
Anderson Patricio
http://blogs.msexchange.org/patricio
Twitter: @apatricio