add the link, visited, and active states to the CSS. Sometimes IE6 needs specific declarations based on other portions of CSS code.
Code:
a.navigation_home:link, a.navigation_home:visited {
display: block;
margin: 0px 0px 0px 100px;
height:30px;
width:64px;
background-image: url(navigation_home.gif);
background-repeat: no-repeat;
}
/* Home Button -- Hover */
a.navigation_home:hover a.navigation_home:active {
background-image: url(navigation_home_hover.gif);
}