1) Think about when you were brand new. When you think about how you'll teach the class think about teaching the "you" that you were when you first started. Think about the things you didn't know and about the types of information you wish had been imparted.
2) SHOW them, don't TELL them. I took a Pow Wow "Ceremonies" class where the entire class was spent having the dude tell us why Ceremonies were important. Um. DUH! We wanted to know HOW TO DO THEM! We wanted to SEE some Ceremonies in practice! If he had spent 15 minutes going over when/why/where and spent the other 40 minutes throwing actual ceremonies at us, we'd have been in heaven.
Think on this: standing in front of a room full of six-year-old boys and telling them "You can earn lots of cool stuff in Cub Scouts!" is fine. Maybe even interesting. But SHOWING them the cub scout sign, the cub scout salute, and getting them to recite the cub scout motto and then telling them, "Awesome, you're most of the way through earning your Bobcat Badge," actually SHOWS them how easy and fun it is!
3) That brings me to the most important point – BE VISUAL!! Bring props or printouts or handouts or or even some sort of swag (one teacher gave us bookmarks with his info on them that were realy cute/creative) to make it visual and memorable. I still have all the printouts from all the events I've ever attended (that were worth keeping – some admittedly got tossed for irrelevance).
4) MAKE IT FUN? :) Be as silly/fun/excited with the adults as you would with the kids. Remember – when you go to Pow Wow as a student, you're there to be an eight-year-old boy for the day and see the world through their eyes, so make sure you treat your students the way you would your Cub Scouts. Sure, give practical applications for making the new system work, but also remember that it's all about the little bits of whimsy and magic that make our world so interesting.
You've never had a problem showing your passion about Scouting, and trust me, it's contageous. Relax and have fun with it yourself, and they'll have fun, too.
5) KEEP IT SIMPLE. Think about it… no one reads their electronics manual. No one reads their vacuum cleaner manual. We just plug stuff in and GO. That's why so many companies have gone to having "quick guides" – just one or two page simple instructions that get you started with the basics. Give them little bite sized ways to get into the habit of making use of the program and/or making it fun.
You're going to do great! And I expect a full report after you're done! ;)