Una base da cui partire:
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN">
<html>
<head>
<title>test</title> 
<script type="text/javascript">
function evidenzarighe(){
var Tabella = document.getElementById("tab").getElementsByTagName("td")
for(var i = 1; i<Tabella.length; i++){
if(Tabella[i].innerHTML >= 10)Tabella[i].style.backgroundColor='red';
}
}
</script>
</head>
<body>
<table width="400" border="0" id="tab">
  <tr>
    <td>1</td>
  </tr>
  <tr>
    <td>2</td>
  </tr>
  <tr>
    <td>3</td>
  </tr>
  <tr>
    <td>4</td>
  </tr>
  <tr>
    <td>5</td>
  </tr>
  <tr>
    <td>6</td>
  </tr>
  <tr>
    <td>7</td>
  </tr>
  <tr>
    <td>10</td>
  </tr>
  <tr>
    <td>11</td>
  </tr>
  <tr>
    <td>12</td>
  </tr>
</table>Evidenza

</body>
</html>