I've been just working on a new website's design and throughout my website i used only PNG images. When i tried in in IE6 i was shocked. I new there was a fix for PNG transparency, but that means additional script code and i need to keep my website's size as little as possible. So i thought of changing all images to GIF. But at first all looked ugly and jagged. I played a lil bit with the output options and found my GIF images looked best when using the following configuration:

Palette->Local(Adaptive); Colors->256; Forced->None; Transparency->Checked; Matte->Custom->Color of the background your image will sit on; Dither->None.

To detect the color of the background where the GIF image will sit on, i used a little applcation called ColorPic.It's free and works very well.