Can anyone suggest a secure IM client? One that's encrypted?
You can try Brosix www.brosix.com. It is a corporate instant messenger built with security in mind. It encrypts all the traffic and whenever possible establishes direct connection between you and the buddy you want to excahnge
files, video, voice etc.
Brosix.com offers you to build your own Instant Messaging network. But if you don't need an IM network, then you can use their free public network
www.brosix.net This is the free version of the corporate messenger, with all of its features, but it is running on a separate network opened for everyone.