方法1：
<script>
function overIt(){
    var the_obj = event.srcElement;
    if(the_obj.tagName.toLowerCase() == "td"){
        the_obj=the_obj.parentElement;
        the_obj.oBgc=the_obj.currentStyle.backgroundColor;            the_obj.oFc=the_obj.currentStyle.color;
        the_obj.style.backgroundColor='red';
        the_obj.style.color='blue';
        the_obj.style.textDecoration='underline';
    }
}

function outIt(){
    var the_obj = event.srcElement;
    if(the_obj.tagName.toLowerCase() == "td"){
        the_obj=the_obj.parentElement;
        the_obj.style.backgroundColor=the_obj.oBgc;
        the_obj.style.color=the_obj.oFc;
        the_obj.style.textDecoration='';
    }
}

</script>

<table border=1 width=400 onmouseover="overIt()" onmouseout="outIt()">
<tr bgColor=#222222> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#333333> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#444444> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#555555> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#666666> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#777777> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#888888> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#999999> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#aaaaaa> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#bbbbbb> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#cccccc> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#dddddd> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#eeeeee> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#ffffff> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
</table>

方法2：
<script>
function overIt(o)
{  o.style.backgroundColor='red';}
function outIt(o)
{  o.style.backgroundColor='';}
</script>
<table border=1 width=400>
<tr bgColor=#222222  onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#333333 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#444444 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#555555 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#666666 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#777777 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#888888 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#999999 onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#aaaaaa onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#bbbbbb onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#cccccc onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#dddddd onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#eeeeee onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
<tr bgColor=#ffffff onmouseover="overIt(this)" onmouseout="outIt(this)"> <td>aaa</td><td>aaa</td><td>aaa</td><td>aaa</td></tr>
</table>