Tutorial found by Arcana here.

First Paragraph follows:

When designing web pages, you will often wish to incorporate graphic elements. The easiest way to include graphics is through the use of images.
Images, though, have two fundamental limitations for supporting graphic elements. First, rather than being vector-based (as are text and graphics created in programs such as Illustrator), images are a collection of pixels. Second, images are always rectangular.
In order to make your graphics look as smooth and accurate as possible, and in order to seamlessly integrate them into your design, you will need to understand antialiasing, and how it relates to transparency. This tutorial will explain the basics of antialiasing, and how to use succesfully use it in tandem with transparency.