If you use Fiddler (an HTTP debugging utility) you'll be able to see all the requests happening behind the scenes.  On that note I noticed you're using one of my modules for the PNG transparency which FireFox, Opera, Safari, don't have an issue with -- only IE6.  The module detects the browser and selectively loads the script necessary only when the browswer needs to use it -- hence you don't see the behavior in FireFox and Chrome.  Looks like I need to fix it in IE7 though... it shouldn't load there either.

At any rate, if you use a very broad CSS selector to apply the fix to your images (like the sample in the documentation and the pre-filled option in the module) you'll see it attempt to apply the fix to everything (jpg, gif, etc).  Obviously that is a behavior you don't want and, as such, you should apply the selector to a very specific range.  In other words, you could do #dnn_dnnLOGO_imgLogo { [insert SW.IEPNG rules here] } to apply it to your logo.  I don't see any other PNG images on that page so using that single line would apply it only to that image and nothing else.  Feel free to contact me directly for more assistance on this.