We all know that IE 6 don't support transparent png images - there is a simple fix for it, called pngfix.js, which you simply add to your scripts by:
<!--[if lt IE 7]> <script defer type="text/javascript" src="pngfix.js"></script> <![endif]-->
in <head> section of your site. The bigger problem occurs when you have to use swfobject.js on your site along with pngfix.js. Suddenly you don't see transparency in png's in IE. The easy way to correct this is to use pngfix.mod.js, which I originally found on http://maxtoroq.wordpress.com/2007/03/23/problems-with-pngfixjs-when-using-swfobjectjs , but script posted there has a lot of special quotes, which makes it not working. Since I could not find working version of the script, I decided to correct the one I found.
I am not the author of the script nor I don't know JavaScript, what I did was to change some typographic quotes.
You can download the file here: pngfix.mod.js
The way to use it is:
<!--[if lt IE 7]> <script defer type="text/javascript" src="pngfix.mod.js"></script> <![endif]-->
in the <head> section of your site, where src has to be obviously corrected to the location of js file.
I strongly suggest wordpress article mentioned above as source of information about the script.
Jacoor