You don't find too many details about Kowloon floating around, which is a shame since it was quite a unique settlement.

The best source of information about it is probably a photo essay called "City of Darkness" (http://www.amazon.com/City-Darkness-Life-Kowloon-Walled/dp/1...) which is frequently out of print, but which I highly recommend if you can snag a copy. It's a fascinating historical document in its own right, and one of the few reliable sources of information about the walled city, which is why it's referenced so heavily in the Wikipedia article.