This is a great “set it and forget it” IE PNG Fix:
This script adds near-native PNG support with alpha opacity to IE 5.5 and 6. Now you can have full translucency and no more ugly grey borders! It requires only one line in your CSS file, and no changes to your website HTML.
<IMG>tags and background images are both supported.
Haven’t had to use something like this in a long while, but this looks like a much better method than the other purely CSS or JavaScript techniques I’ve seen.