The big IM companies don’t particularly care for third party clients like Pidgin accessing their network, but I say to hell with them! Most refuse to offer viable Linux clients to their service. Yahoo at one time had provided a Linux client, but has not maintained it. However, the pidgin version provided by Lenny does not connect to Yahoo, because Yahoo periodically changes there login protocol to discourage third party clients. The backport of pidgin is likewise outdated, however someone has been nice anough to provide backports of Pidgin 2.5.7 packages for 32bit systems. You will need:

pidgin-data
libpurple
pidgin

Now change directory to where you downloaded these. Fist install pidgin from the regular repositories so you will have the proper dependencies. Then uninstall pidgin and pidgin-data to make way to install the updated versions.

sudo apt-get install pidgin
sudo apt-get remove pidgin pidgin-data

sudo dpkg -i pidgin-data_2.5.7-1~bpo50+1_all.deb
sudo dpkg -i libpurple0_2.5.7-1~bpo50+1_i386.deb
sudo dpkg -i pidgin_2.5.7-1~bpo50+1_i386.deb

There is great facebook chat plugin for pidgin you can download here. First you will need to install the dependency libjson-glib.

apt-get install libjson-glib-1.0-0
sudo dpkg -i pidgin-facebookchat-1.54.deb