Arrivo tardi?
codice:
<style>
table.#t1 tr {background:#ccc}
</style>

<script>
function Vai() {
  var t1 = document.getElementById("t1");
  for (var i=0; i<t1.rows.length; i++) {
    t1.rows(i).onmouseover = function colora() {this.style.background='#e8e8e8';}
    t1.rows(i).onmouseout = function scolora() {this.style.background='#ccc';}
  }
}
</script>

<body onload="Vai()">
  <table id="t1">
    <tr><td>a</td></tr>
    <tr><td>a</td></tr>
    <tr><td>a</td></tr>
    <tr><td>a</td></tr>
    <tr><td>a</td></tr>
    <tr><td>a</td></tr>
  </table>
</body>