I think doing it all via IRC would be too difficult if there is any more then about 5 people on there, typing out all the questions / responses etc would be very time consuming and inefficient.
I like the idea of having a written tutorial posted online either in a dedicated tutorials area of the site or on the forums, and then having weekly meetings via some VOIP / IRC chat to ask questions. Either Skype if there are just a few people, Teamspeak or Vent if there are more, or Skypecast if there are a lot of people interested. I would defiantly like to learn some more PHP / MySQL over the summer.