Many years ago a collegue and I wrote up our experiences of using NetMeeting to deliver library instruction to distance students:
Pival, Paul R. and Johanna Tunon. “NetMeeting: A New and Inexpensive Alternative for Delivering Library Instruction to Distance Students.” College & Research Libraries News. 59(10) (November 1998), p. 758-760.
Haven’t really done any experimentation with live video delivered to distance students since then, but just came across this site that should do a good job of bringing me up to speed on many of the alternatives. The focus is on the easy and cheap stuff 🙂