[EricH]

Throw everybody at it. If there is a limited number of presenters, have it about half rookies and half veterans, and try to get the rest of the rookies in as observers.

Of course, this does assume that the more experienced presenters take the time to teach the less experienced ones. There are a number of ways to do this, but the best is probably to have everyone give the same presentation to the team in random groups. Then everybody gets a chance to find holes in the presentation and the presenters' style, and fix the issues. Repeat until mostly perfect (about 2-3 sessions).

This sort of thing works well for demos, too. Just make sure that the rookies are up to speed and have a designated expert to direct the tough questions to if they don't know the answer.