but with IE6 still making up a substantial market share, I'd like to cater for it as well as possible
I know. Were it not for that, I'd suggest you just forget it all together. Falling back to a GIF *is* catering it IE6 given that it officially doesn't support PNG at all. But if you really want a PNG, use a really big repeating image, or user layered foreground images. --Erik
