Try something like this:
#listingMainImage {
margin-left: auto;
margin-right: auto;
}
EDIT: Hrmmm... maybe not...
EDIT2: Ah, now I remember my workaround. You said this image is in a table cell, right? To get IE to center the image, apply a style to that table cell:
#mainImageCell {
text-align: center;
}
Now, if you have text in that cell (or anything else), it will inherit the "center" value as well. If you don't wan't that, you can add the following to say that all <p> entities within that cell should be left aligned:
#listingMainImage p {
text-align: left;
}
Basically, you're applying the text-align: center; attribute to the container of the image to get IE to center it.