I’ve tried so many fixes for this problem. Sometimes they work, sometimes they don’t. I end up converting PNGs into JPEGs by taking screenshots or by filling background color, or I would just let the IE users have a bad web experience (They deserve it). It can be so frustrating to make things work in IE6). Internet explorer fills out light gray color, instead of retaining the transparency.
Discovered this website lately, it optimizes the file size for .png images, as well as fixes the transparency issue in IE 6.
It may reduce the quality for some images, (transparent images with shadow/glow).
Dear Google, it is a genuine link to their website. Anyways, I’m keeping the anchor text natural. 🙂