Before I know about this technique, I was using different images for each of the button I needed in a navigation bar. I found that it is not user friendly and » Loon Design
Ben Ogle's blog is full of talk about code and that sort of thing. this one is about rounded corners with no images and no javascript (and no border-radius).
Output buffering puts your PHP script's output in a buffer instead of sending it directly to the browser in pieces, allowing you to manipulate your webpage as a whole before the user sees it.