There's a great tutorial here - it's usually the one I send to new Twisty's :-)
http://krondo.com/blog/?page_id=1327
Its worth remembering that Twisted programming is more of a thinking paradigm than a programming one. Also, it's worth doing away with the client server model too - in Twisted there's just one broker talking in either direction to another.
Take a look here after the above too:
http://twistedmatrix.com/documents/current/core/howto/pb-intro.html
Enjoy :-)