You may find your answers about .PNG file issues and Internet Explorer here:
http://www.alistapart.com/articles/pngopacity/
Also, a nice program/website I found lets you install IE3, IE4.01, IE5, IE5.5, and IE6 all at once. It can help anyone out who would have browser conflicts in their code like I had...
http://tredosoft.com/Multiple_IE
zim2411, have you tried to take a screenshot of how your site should look (Firefox maybe?) and then crop out a new image with the background intact?