"As with most things, a logical and structured approach is the best way to go. Therefore I have put together 10 quick tips (in no special order) to help make your CSS coding as pain-free as possible."
The basic idea of Nifty Corners is to get some coulored lines to get the rounded effect."
Full article: Nifty Corners: rounded corners without images
How to emulate frames using CSS: CSS Frames
How to make accessible rounded tab menus using CSS.