You certainly are not alone with this problem. Many corporate executives break out in cold sweats when they have an important meeting.
There are several things that may help you:

1) Prepare your material but don't memorize it.
Treat your seminar as though you were explaining the material to a friend. Memorizing actually places a lot of pressure on you. A few notes will help.

2) Ask family or friends to be an audience so that you will be able to practice in front of familiar people that are non threatening.

3) Before the seminar, try to relax, have a cup of de-caffeinated tea. Avoid caffeine that day to minimize anxiety.

4) You might put things in perspective by actually confronting the situation. Make a list of the worse possible things that could happen during your seminar. Once they are written down, you may find that your fears are unwarranted.

5) Spend a few minutes each day concentrating on all your good points. Try to stop yourself from thinking negative thoughts. Each time you have a negative thought, rephrase it to make it positive. Attitude is a big component to anxiety.

5) There are herbal formulas that you might try. Formula's containing kava kava tend to relax a person without making them drowsy. These formula's are helpful for intermittent anxiety caused by a situation. Many executives, or public speakers take kava kava formulas before a group meeting. It promotes alertness, yet helps calm anxiety.

Dr. Bob