Wireshark -- tutorials

This is a free tool, usable in both Linux and Windows, for network analysis.
Personally I'm trying to become knowledgeable enough to be able to use it fruitfully so I've been hunting around for some tutorials.
Here are links to Parts I-IV of what's considered a quality tutorial:
Ethereal Tutorial - Part one
Ethereal Tutorial - Part 2
Ethereal Tutorial - Part 3
Wireshark Tutorial - part 4
(yeah, it used to be called ethereal up to 2006)

There are also some useful flv videos of which some of the best I've seen are:
Intro to Wireshark: Packet Capture and Protocol Analysis

Introduction to Wireshark (Part 1 of 3)
Cookies and Grabbing Passwords with Wireshark (Part 2 of 3)