You are going to have to create your design in your graphics program. Get it exactly the way you want it. Then you can insert it into your web design.
You can have a transparent background on the corners to make it appear to be round or make the background color of the graphic the same as the web page background. Designing in the web world is pretty flat. Everything that has layers must be made in a graphics program and then placed in a webpage.

Since you are just learning, learn how to use div's instead of tables. Tables are passe... There are so many great learning sites posted in the css forum sticky. Welcome to the world of web design! Once you overcome the learning curve I'm sure you will enjoy it and create beautiful sites!