[monolithed]

Mark, перед созданием темы поиском пользовались?

<script type="text/javascript">
window.onload = function(){
    var tr = document.getElementById('table').getElementsByTagName('tr'), 
          i = tr.length;
    while(i--) {
        tr[i].style.backgroundColor = i%2 ? 'red' : 'green';
    }
};
</script>
<style>
td {
    border: 1px solid #FFF;
    width: 50px;
    height: 50px;
}
</style>
<table id="table">
    <tr><td>1</td><td>1</td><td>1</td></tr>
    <tr><td>2</td><td>2</td><td>2</td></tr>
    <tr><td>3</td><td>3</td><td>3</td></tr>
</table>