Only do it with an experienced guide. Read Jim Fadiman's book. If you're serious, sincere, and patient you should be able to find a guide through your local yoga, meditation, new age, etc. scene. Michael Pollan's new book is excellent if you need a bit more motivation.

These medicines are far more powerful than you could possibly comprehend. Once you are in it, expect to have zero control, so you need a safe, experienced environment.