Weeeelllll, if you do a right-click then view source you'll see that in this case they're using onmouseover and onmouseout to change the class of the table cell (as shown below). Changing the class between MenuBackground and MenuOver.
<tr
onmouseover="this.oldClassName=this.className;this.className='MenuOver'"
onmouseout="this.className=this.oldClassName"
class="MenuBackground">
As drew010 mentioned, this could be done completely in CSS with the use of one of CSS's dynamic pseudo-classes :hover. This could be used on the table cell class but I have a funny feeling that some browser's (coughIEcough) only allow this on link elements. This also isn't really a problem as you'll notice that whole of the table cell is clickable so the link is stretched to the size of the cell. You could implement the rollover in css with the following code.
.PlayerHighlight {
background-color:#000000;
}
.PlayerHighligh:hover {
background-color:#ffffff;
}
Now that you've seen how usefull it can be. hopefully next time you'll RTFS (read the fudging (it's a family show OK?) source).