function highlightRow(obj, over) {
	rowObj = obj;
	for (i = 0; i < rowObj.childNodes.length; i++) {
		rowObj.childNodes[i].className = (over) ? 'HOVERrow4' : 'Media_row4';
		var other=rowObj.childNodes[i].getElementsByTagName('a');
		for(var i=0;i<other.length;i++){ other[i].className = (over) ? 'a' : 'txtlink'; }
	}
}

<tr onmouseover='javascript:highlightRow(this, true)' onmouseout='javascript:highlightRow(this, false)' onclick="javascript:go('?r=readme.txt')">
<td class="Media_row4" width=30 align="center" valign="middle" ><img src="/images/dir_images/txt.gif"></td>
<td class="Media_row4"><div class="sidebitsize0">132 B</div><span></span><div><span class="row4"><a class="txtlink">readme.txt</a></span></div></td>
<td class="Media_row4" width=120 align="center" valign="middle" nowrap="nowrap"><span class="gensmall">Sep 17 06</span></td>
</tr>