用css + javascript 應該很簡單吧
像下面這樣...
<html>
<head>
<title>字型變換</title>
<style>
<!--
.font1 {font-family: Arial; font-size: 14pt;}
-->
</style>
</head>
<body>
<table border="0" cellpadding="3" cellspacing="0" width="300" align="center">
<tr><td nowrap id="f1" class="font1" width="100%" align="center">
<a href="javascript:;" onclick="f1.style.fontFamily='細明體'">123,abC 細明體</a>
<a href="javascript:;" onclick="f1.style.fontFamily='標楷體'">123,abC 標楷體</a>
</td></tr>
</table>
</body>
</html>