You certainly aren’t alone. According to The Book of Lists, public speaking is the number one fear for most people, coming in ahead of fears of death and maiming!
It’s great that you want to overcome this. The keys to success are facing your fears, practicing, and identifying areas of improvement. Practice is essential and will help you gain confidence about appearing in front of people. But becoming a really polished, persuasive speaker is easiest if you have someone to give you feedback and help you improve.
Elly suggests you join a group such as Toastmasters, which has clubs all over the country. Members meet once weekly or twice a month, often at breakfast or lunch, and focus on improving personal communication skills. Or you could take a presentations short course in your community.
If you are determined to do this on your own, at least enlist the help of a friend who can watch you speak and then help point out what worked well and what needs improvement. There are plenty of reference books and Internet sites on this topic. Taping your practice sessions for review is a very effective, albeit painful, strategy.
Public speaking is a skill that will serve you well even beyond your work with the PTO. I think you will find this very rewarding. Good luck!
Toastmasters: http://www.toastmasters.org