You could not set the width by modifying the filter you've used.
AlphaImageLoader Filter has limited objects which do not include setting the width.
If you want to set the width of your picture, you could put the picture in a container like div and set the "width" attribute to achieve your requirement.
For more about the related problem, you could click the following thread links. Maybe you could get some ideas from them.
1.How do I make background-size work in IE?
2.progid:DXImageTransform.Microsoft.AlphaImageLoader causing links to be unclickable in ie8, ie7, and ie6
I've made a sample and you could refer to.
CSS.
.imageWrapper {
display: block;
width: 80%;
height: 500px;
background-image: url(Images/test2.jpg);
background-repeat: no-repeat;
filter: progid:DXImageTransform.Microsoft.AlphaImageLoader( src='Images/test2.jpg', sizingMethod='scale');
-ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader( src='Images/test2.jpg', sizingMethod='scale')";
}
.ie6 .imageWrapper,
.ie7 .imageWrapper,
.ie8 .imageWrapper {
background-image: none;
}
HTML.
<div class="imageWrapper">
testtesttesttest
testtesttesttest
</div>
EDIT: Here is my wroking result:result