You can use :
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(
src='images/logo.gif',
sizingMethod='scale');
-ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(
src='images/logo.gif',
sizingMethod='scale')";
But if you use sprites you can have some issues...
Sources : AlphaImageLoader Filter @microsoft