I have read some of this book and I don't like it that much. I personally feel the author spends too much time with things that are pretty easy to compress.
Looking backwards I think the Jabber documentation is enough to write an IM client. I wrote one for alarming purposes. This is the first edition and the book has plenty of errors in the text. ( The code samples seem to be O.K.). Obviously the author was so busy pushing out his book that he didn't let anyone proofread it.

I would recommend to buy another book ( there are plenty ) or rely on the Jabber documentation and the plenty of samples the web has to offer.