"How do you address technical questions that you simply don't know the answer to?"
You want to be straight-forward in an interview, and not attempt to talk your way out of a difficult question (a la many politicians today).
The best way to prepare for this is to understand the position and study the job description. From there, anticipate questions that cover areas that you are not as strong in. When they come up, answer truthfully that the question deserves a response that you can not fully produce, but that it is an area of interest to you, and you plan to pursue and learn more about.