Replace a form submit button with an image using just CSS

form input[type=submit] {
    background : url(../images/submit.gif) no-repeat center center;
    width : 90px;
    height :42px;
    border : none;
    color : transparent;
    font-size : 0margin: 0px;
    padding: 0px;
    float: right;
}
adapted from http://www.suburban-glory.com/blog?page=140