Intendi questo?

codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Documento senza titolo</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<script language="JavaScript">
var previousTRClicked = null; 
function clicca(aTR) {
if (previousTRClicked != null) {
  previousTRClicked.className = "notClicked";
 } //  if (previousTRClicked != null) 
 aTR.className = aTR.className == "notClicked" ? "clicked" : "notClicked";
 previousTRClicked = aTR;
} // function clicca(aTR)

</script>
<style>
.clicked    {
	background-color:navy;
	color:white;
	font-family: Verdana, Arial, Helvetica, sans-serif;
	font-size: 10px;
	font-weight: bold;
	text-decoration: none;
}
.notClicked {
	color:#000000;
	font-family: Verdana, Arial, Helvetica, sans-serif;
	font-size: 10px;
	text-decoration: none;
}

</style>
</head>

<body>
<table border="1">
	<tr onClick="clicca(this)" class="notClicked">
		<td>
		riga 1 - cella 1
		</td>
		<td>
		riga 1 - cella 2
		</td>
	</tr>
	<tr onClick="clicca(this)" class="notClicked">
		<td>
		riga 2 - cella 1
		</td>
		<td>
		riga 2 - cella 2
		</td>
	</tr>
	<tr onClick="clicca(this)" class="notClicked">
		<td>
		riga 3 - cella 1
		</td>
		<td>
		riga 3 - cella 2
		</td>
	</tr>
</table>
</body>
</html>
Bye