NOTE: This post was originally made on the same date in 2005, not 2006.
In July 2004, I attended and presented at the 5th HOPE conference in NYC. The subject of my presentation was "AS/400: Lifting the veil of obscurity" which was an introduction to the AS/400, how it works, and where common mistakes are made from an administration standpoint.
While the MP3 audio version has been available for some time, it appears that 2600 magazine (the people who run the conference) have made all of the videos available on their web site now as well.
You can get a copy of my presentation for $5.00 on SVCD at the 2600 store. The entire list of presentations is at this page. I also made a 5-10 minute appearance on sl1pm0de's excellent "hacker radio" presentation as well, so I recommend you pick that up while you are there.