Most web developers are aware of the IE alpha transparency problems with PNG images; or will be before long. A lot of developers use GIF images rather than the superior PNG format for this reason; which is a shame.
I was discussing the issue with Alex over at Prettier Pixels (a talented UK freelance website designer and builder) and he suggested this nifty IE PNG fix by TwinHelix that you can use to avoid the issues. Thanks Alex!
I long for the day when IE 6 support is no longer required!