input.button{
width:114px;
height:37px;
border: none;
background: transparent url(images/submit_btn.gif) no-repeat center;
overflow: hidden;
text-indent: -999px;

/* this text sorts text indent in IE6 */
font-size: 0px;
display:block;
line-height: 0px;	

}

http://www.productivedreams.com/ie-not-intepreting-text-indent-on-submit-buttons/

Allows custom background images for submit buttons in ie6

Using a background image for submit buttons in IE6

css, ie6

CSS