IE6 Selectors issues

IE6 Selectors issues

My site actually works okay in other browsers but when I checked in IE6,
there is a problem. In my global navigation, I clicked this certain page.
For example, I clicked ABOUT ME page. My global navigation changes its
image when the page is active. Like it has a different color from inactive
pages. In IE6, when I'm in the current page, ABOUT ME, the current image
in the global navigation is different. Say, it's CONTACT US. But when
hovered, the image that appears is correct.
This is the snippet of CSS:
.cat-item-5 {
float: left;
display: inline;
width: 162px;
height: 48px;
text-indent: -30000px;
background: -639px 0 url(images/menu.png) no-repeat;
}
.cat-item-5 a {
display: block;
width: 162px;
height: 48px;
background: -639px 0 url(images/menu.png) no-repeat;
}
.cat-item-5 a:hover,
.cat-item-5.current-cat a {
background: -639px 0 url(images/menu_o.png) no-repeat;
}
Hope you can help me, thanks!