I have similar problems adressing large groups, but as I have had to do presntations monthly for the past year and a bit at uni, i'm getting slightly more comfortable with it --> a few things i'v found to help:

Stand up and walk around - I get nervous, and by moving around I relieve stress and (I think) keep people's attention

Learn the stuff really well - i'v done some presentations and discussions with very little prep, and it is far more uncomfortable. If you know alot about the subject, you know your opinions on the issues are valid, and are better able to discuss them.

Discuss the topic with a friend or family before you do the presentation, so you have an idea of how people might respond.

Look and the corners of a room - I find it really difficult to maintain eye contact with people, and was told by a freind to look at the corners of rooms as it gives people the impression that you are looking towards them. If you have any friends in your class you can aks them to help you out with questions, or to help you start discussion.

Speak deliberately loudly, clearly and slowly.

Smile like a maniac.

In terms of the stage fright thing, I found practice really helped, and also a few drinks before-hand, (enough to relax, but not inhibit performance)