"The fix allows IE to properly render PNG alpha transparency. If you want to get straight to the script, go to the how-to page and follow the instructions there.
Why only versions 5.5 & 6? Because Windows IE versions prior to 5.5 do not support the filter which fixes the PNG problem, and version 7 (not yet released at the time of writing in January 2006) is reported to have fixed the issue entirely."
The PNG has been out for quite some time and sites like Apple.com, Adobe.com and Macromedia.com are full of them. I'm surprised that Macromedia did not include this as an additional command for Dreamweaver. Thanks a lot, Bob! PNG in Internet Explorer: How to Use