I think many people/developer/designers face a problem while working on transparent .png images and the Internet Explorer 6. The IE6 do not recognize the .png images and treat them somewhat similar to non-transparent images.
That's generally the best way to fix it, assuming your PC won't run IEvil 7 or beyond.
My general recommendation is to switch to FireFox anyways. I once ran it on a Compaq mini-tower running Windows 98...first edition...and it ran better than the native IEvil version (which was, if I remember correction, one of the original installations of the IE5 series with Active Desktop functionality).