I can't count the number of times I've listened to someone talking in a tech/geek/nerd discussion and thought, "Dang, they should be a presenter!" Yeah, yeah, I know, the most common fear is that of public speaking....forget that, folks. You can do this. It's an awesome experience, whether one presents at a small local meeting or a national conference.
Ask around; there's probably a User Group of some description in your area, and I can almost guarantee that they'll have an opportunity for you to present a topic.
All I can say is - go for it.