You do mean alcohol?

On a more serious note: If your freezing up because you're nervous, I always find it is helpful to make other people nervous, then you are not alone, and become less nervous.
For example, if your in a class where people are giving speeches and your nervous because you did no research on your topic, and are planning on winging it. Start talking to the other people who will also give speeches, and bring up the fact that there grade depends on the speech, the teacher is expecting excellence, or just some other tension mounting thing. This fact might mount your own tension some, but one of the most calming experiences is to watch someone else freak out.
(As a side note, it is also a neat idea, grade wise, because nervous people generally give bad presentations, and lowing the rest of the classes grade creates a better chance that your grade will be curved upward. )

OF COURSE there is the chance that you aren't getting nervous from a required project. In this case, don't feel like you have to speak. I often times (almost always) find people who say nothing a whole lot more appealing than those who talk a lot. If you still can't stand silencing yourself but are too nervous to speak, wait a few years until your balls drop.