This is completely off topic in regards to email and will only interest paranoids and crypto-freaks, but you can expand your GnuPG setup to encrypt IM's over Gaim. Gaim-e gets GnuPG and Gaim talking and allows you to secure your MSN messages, and it might do other protocols too, I just don't remember at the moment. Be warned if you do play with it, its a hog on system resources if you have a massive key.

http://gaim-e.sourceforge.net/