it's a fucking hack but it can be useful

max-dimensions for IE6

// maxheight + maxwidth
img {
    /* For good browsers :) */
    max-height: 510px;
    max-width: 510px;
     /* Feed the devil :) */
    width: expression(this.offsetWidth>=this.offsetHeight?Math.min(500, this.offsetWidth) : 'auto');
    height: expression(this.offsetHeight>this.offsetWidth?Math.min(500, this.offsetHeight) : 'auto');
}

// maxheight
img {
    /* For good browsers :) */
    max-height: 500px;
     /* Feed the devil :) */
    height: expression(this.height>510?500:true);
}

// width
img {
    /* For good browsers :) */
    max-width: 500px;
    /* Feed the devil :) */
    width: expression(this.width>510?500:true);
}