A bit late, but this could also be useful. There is an IE filter, for IE 5.5+, which you can apply:
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(
src='images/logo.gif',
sizingMethod='scale');
-ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(
src='images/logo.gif',
sizingMethod='scale')";
However, this scales the entire image to fit in the allocated area, so if you're using a sprite, this may cause issues.
Specification: AlphaImageLoader Filter @microsoft
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