Surrey Linux User Group
http://voipspeak.net/index.php?/content/view/33/2/ free book.
Or, as they put it more eloquently on that page:
This needs someone to write something better, such as a list of good links, but meanwhile here are some tips from the mailing list:
Try turning off your firewall: iptables -F
Or install the gui Firestarter, which will show you what connections are being attempted.
Recommended docs: http://www.samba.org and in particular http://us2.samba.org/samba/docs/man/Samba3-ByExample/simple.html