请教

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title> new document </title>
    <meta name="generator" content="editplus" />
    <meta name="author" content="Gao YiXiang" />
    <meta name="email" content="[email protected]" />
    <meta name="keywords" content="javascript dhtml dom" />
    <meta name="description" content="I love web development." />
</head>
<body>
    <span id="spnShow">变、变、变</span>
    <script type="text/javascript">
    <!--
var oShow = document.getElementById("spnShow");
oShow.onmouseover = function()
{
    this.style.fontSize = "18px";
    this.style.color = "red";
    this.style.fontWeight = "bold";
};
oShow.onmouseout = function()
{
    this.style.fontSize = "14px";
    this.style.color = "black";
    this.style.fontWeight = "normal";
};
    //-->
    </script>
</body>
</html>送你三本手册！DHTML参考手册
http://download.csdn.net/source/308913样式表中文手册
http://download.csdn.net/source/304124JScript语言参考
http://download.csdn.net/source/308916入门级教程可以看这个 
http://www.w3schools.com/ 
中文版 
http://www.w3school.com.cn/