Why it’s usually no biggie.
As I’m sure you are aware, IE 6 doesn’t fully support transparent PNGs and generally display them with ugly gray backgrounds. Generally this can be solved by using a filter that IE does support as follows:
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="theimage.png", sizingMethod="crop");
There’s also a brilliant solution that avoids the filter and can be used through the DD_belatedPNG script.