代码是从网上摘抄的，感觉应该显示的样字和代码描述的不一致，不过实际上这样的效果正是我要的，所以就没修改了，哈哈！
晕，今天才发现在FIREFOX和IE上显示的效果不一样，不好意思，效果没达到，请各位看官收下留情。文章就不删了！
<html xmlns="http://www.w3.org/1999/xhtml">
<head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>
</title>
<script language="javascript" type="text/javascript">
function DoAlert() {
alert('管他，能用就行！');
}
</script>
</head>
<body>
<input id="TestAlert" type="button" onclick="DoAlert()" value="TestAlert" />
</body>
</html>
<script type="text/javascript">
window.alert = function (txt) {
document.write('<table width="300" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC">');
document.write(' <tr>');
document.write(' <td align="center" bgcolor="#CCCCCC">操作提示</td>');
document.write(' </tr>');
document.write(' <tr>');
document.write(' <td bgcolor="#FFFFFF">' + txt + '</td>');
document.write(' </tr>');
document.write(' <tr>');
document.write(' <td align="center" bgcolor="#FFFFFF"><input type="button" name="Submit" value="返回" onclick="window.history.go(-1)"/>');
document.write(' <input type="button" name="Submit2" value="关闭" onclick="window.close()"/></td>');
document.write(' </tr>');
document.write('</table>');
</script>
<head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>
</title>
<script language="javascript" type="text/javascript">
function DoAlert() {
alert('管他，能用就行！');
}
</script>
</head>
<body>
<input id="TestAlert" type="button" onclick="DoAlert()" value="TestAlert" />
</body>
</html>
<script type="text/javascript">
window.alert = function (txt) {
document.write('<table width="300" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC">');
document.write(' <tr>');
document.write(' <td align="center" bgcolor="#CCCCCC">操作提示</td>');
document.write(' </tr>');
document.write(' <tr>');
document.write(' <td bgcolor="#FFFFFF">' + txt + '</td>');
document.write(' </tr>');
document.write(' <tr>');
document.write(' <td align="center" bgcolor="#FFFFFF"><input type="button" name="Submit" value="返回" onclick="window.history.go(-1)"/>');
document.write(' <input type="button" name="Submit2" value="关闭" onclick="window.close()"/></td>');
document.write(' </tr>');
document.write('</table>');
</script>