
The PNG (Portable Network Graphics) graphic format was developed in the mid-1990s, and it has four main advantages over the GIF format for use on the Web:
Unfortunately, Internet Explorer does not support transparent PNG images, but now, thanks to TwinHelix Designs, it is possible to display transparent PNG images in IE5.5+.
Below are two images on top of a checkerboard background. The image on the left is what a transparent PNG looks like in Internet Explorer without the Alpha Fix. The image on the right has the Alpha Fix applied:

You can read more about the Alpha Fix and download it here.