If you want to greatly improve your PowerPoint presentation, the slide show: Death by PowerPoint outlines very practical ways to do so.
The author, Alex Kapterev communicates some simple ideas that most people could manage without advanced PowerPoint techniques. Kapterev is Russian, so some of his examples of bad slides are in Russian. They don't look a great deal more incomprehensible than many I have seen written entirely in English.
Once again, I found this connection on Paul Giber's attractive and practical blog: Powerful Presentation Techniques.