We all have faced this problem during HTML development. Internet Explorer 6 renders transparent PNG images in different way. It puts some other color , it damages the design.
One solution is create gif images for IE6 and mention those in separate style sheet file for IE6
You can download that library from : http://www.twinhelix.com/css/iepngfix/
You can see an online demo and usage here:
Remember to add that htc file inside your style sheet or like this: