一个页面中2个table，如何实现鼠标放上去的时候2行背景色同时改变，还有个新问题

<TABLE border='1' width="120" id="tb1"onmouseover="this.style.background='#66CC00';document.getElementById('tb2').style.background='#66CC00';" onmouseout="this.style.background='#ffffff';document.getElementById('tb2').style.background='#ffffff';">
  <TR>
<TD>aaaaaaaaaaaa</TD>
<TD>aaaaaaaaa</TD>
  </TR>
  <TR>
<TD>aaaaaaaaaaaaa</TD>
<TD>aaaaaaaa</TD>
  </TR>
  </TABLE>
  <TABLE border='1' width="120" id="tb2" onmouseover="this.style.background='#66CC00';document.getElementById('tb1').style.background='#66CC00';" onmouseout="this.style.background='#ffffff';document.getElementById('tb1').style.background='#ffffff';">
  <TR>
<TD>bbbbbbbbbb</TD>
<TD>bbbbbbbbbbbbbbbb</TD>
  </TR>
  <TR>
<TD>bbbbbbbbbbbbbbb</TD>
<TD>bbbbbbbbbbbbbbbbbbb</TD>
  </TR>
  </TABLE>
 </BODY>
</HTML>