I've been debating creationists for nearly 20 years now. I've learned a few things.
The next few BLOG entries will discuss my recommendations for how to win such debates (or, at least, how to have fun in those debates).
My first recommendation is to not engage in an oral debate. In general creationists might tend to throw questions at you for which you don't have answers. But since creationism is totally fraudulent, rest assured that there are answers. But often a little research is required. Engaging in a written debate allows such research to be performed. Learn how to do such research.
The first place that I typically look when I'm challenged with a claim that I have never seen before, is the talkorigins web site. Do a search there. I'm confident that well over 90% of all creationist claims have been refuted on that site.
Good luck and have fun! I know that I've had a lot of fun debating creationists.