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.
For this there is pngfix code available on the internet. Its a Javascript code that solves the problem of .png images for IE6. Its a free code available on the internet and can be found easily. The site from where you download the pngfix.js code also gives the instruction of about how to use it.
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).