I don't remember who was talking about this on this forum, so I decided to start a new topic...
I found this http://www.silcnet.org/ that is supposed to be an encripted/secure pidgin... I don't know if it's totally GPL (at least pidgin is) and I don't know if it's portable or can be made portable... I'm just posting for information on interested people, since somebody in the past talked about this feature with pidgin.
[Moderator's Note: All comments on this post made after July 24, 2007 were inadvertently removed during forum cleanup. The full thread is accessible via Archive.org's Wayback Machine. Our apologies for the inconvenience.]
If you check the beta forums where the Beta 1 of Pidgin 2.0.2 is being done, there's an installer for the Pidgin Encrypt plugin on there. That enables secure, encrypted IM. Haven't tried SILC so I don't know how its plugin works. OTR used to be the encryption method of choice for Gaim Portable, but the new release is un-portable, so we're recommending Pidgin Encryption now.
UPDATE: SILC is included in Pidgin itself, so no need to think about it as an add-on.
Sometimes, the impossible can become possible, if you're awesome!