Is it possible to make your power point stuff an actual outline of your talk, with subheadings and so forth? I'm thinking of something like: I. Heredity As A Possible Factor; A. Examples From the Literature; 1. Story of the 2-Headed Boy; 2. .....Definitely any mnemonic techniques such as acronyms and acrostics can help.

Also, I agree that practice is important, but try not to worry if you don't end up presenting it word for word, as long as you get the information correct. Of course, try to use voice inflection and make it interesting. Concentrate on the fact that you are telling the folks interesting stuff, just like you would be telling friends, except likely in a more organized way!