dunque...non so' se sia compatibile con tutti i browser... cmq così non hai bisogno di mettere mille ID:


<HTML>
<HEAD>
<style>
#tabella {text-align:right;background-color: yellow}
#tabella td {background-color:lightblue;}
</style>
<script>
function Cambia(id,val) {
id.style['background']=val;
}
</script>
</HEAD>
<BODY>
<table ID="tabella" width="50%">
<tr>
<td onmouseOver="Cambia(this,'white')" onmouseOut="Cambia(this,'lightblue')">1</td>
</tr>
<tr>
<td onmouseOver="Cambia(this,'white')" onmouseOut="Cambia(this,'lightblue')">2</td>
</tr>
<tr>
<td onmouseOver="Cambia(this,'white')" onmouseOut="Cambia(this,'lightblue')">3</td>
</tr>
</BODY>
</HTML>