Marc Charbonneau

Short answer: you can’t. In my experience it’s easier to just use 8bit PNGs when you absolutely need transparency (a nav menu for instance, where the background color changes depending on the context), and fake alpha transparency by layering the image over the background in photoshop. Of course, this can have plenty of problems by itself depending on the complexity of your design, but at least it’s clean and you can be sure it will work on any platform.

If you really need alpha transparency, and don’t mind marking up your code a bit, give this article a try.