It may be easier, but it wouldn't be as good. You'd have to resort to "downlevel-revealed" conditional comments at best, which would render your page invalid.
P.S. I did a lot of research and I found a lot of scripts that show how to display the PNG in IE using a filter but I can't get any of them to work properly so I feel that using GIF alternatives would be an easier method.
If you can get one of those filter hacks working, it's best to do so:
/EDIT: From that link, LOL.
<!-- Head: -->
<!--[if IE]><style type="text/css">
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src='firstAlphaImage.png', sizingMethod='scale');
background-image: url(firstAlphaImage.png) !important;
<!-- Body: -->