I had to give a speech at mine, too. I just graduation this May, but thankfully I went to a really small school. My graduating class was barely over 50 people, so people at least knew who I was. But that didn't make it any less terrifying. For me, the worst part was the anticipation. During the actual ceremony, I was fine. All they did after speeches was call each person's name, people clap, you walk across the stage, and then sit back down. Not a big deal. Then after the ceremony, we all lined up outside to shake hands with people and such. I don't think a lot of other schools do this, though.
The important thing to remember is that you probably won't have to see any of these people ever again. So who cares if they don't know you now? Just write a good speech and practice a lot.