I want to create an android Facebook chat application , i found this open source project .. http://coderrr.wordpress.com/2008/05/06/facebook-chat-api/
but i want to ask
There is great simple code https://github.com/KanybekMomukeyev/FacebookChat , i used it in my app.
Facebook provides their own chat API. See the docs at Integrating with Facebook Chat. They provide sample code in PHP.
You can also use Jabber to authenticate with Facebook. You'll need an application key to ensure this all works.
Dig a bit deeper into http://developers.facebook.com/docs/chat/. There are a number of XMPP and related APIs for Java, C#, iOS, and Android alike to be found on the web - or you can base such work on the libpurple API from Pidgin (http://www.pidgin.im/). It would behoove you to become familiar with XMPP concepts.