鼠标一点 文字消失 的有关问题

鼠标一点 文字消失 的问题
请问大大们，如果鼠标一点文本框 文本框的默认值 就消失了，然后鼠标点别的地方，文本框又会自动显示默认值，这种效果该怎么做？
我上网搜了很多，用javascript写的，或者是onclick,onblur之类的我都试过，如果是纯html是可以用，但是写在php里面就一点作用都没有！这很奇怪啊！为什么？
代码如下：

JScript code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/--><script language="JavaScript" type="text/javascript">   function addListener(element,e,fn){            if(element.addEventListener){                 element.addEventListener(e,fn,false);             } else {                 element.attachEvent("on" + e,fn);              }       }   var txt_oldPsw = document.getElementById("txt_oldPsw");   addListener(txt_oldPsw,"click",function(){txt_oldPsw.value = "";})   addListener(txt_oldPsw,"blur",function(){txt_oldPsw.value = "old Password";})   var txt_newPsw = document.getElementById("txt_newPsw");   addListener(txt_newPsw,"click",function(){txt_newPsw.value = "";})   addListener(txt_newPsw,"blur",function(){txt_newPsw.value = "new Password";})   var txt_reenter = document.getElementById("txt_reenter");   addListener(txt_reenter,"click",function(){txt_reenter.value = "";})   addListener(txt_reenter,"blur",function(){txt_reenter.value = "re-enter new password";})</script>

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PHP code

<!--Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->echo "<tr><td><input class="txt_style" id="txt_oldPsw" style="font-size:10.5pt; color:#6b6b6b" type="text" name="txt_oldPsw" value="old password"></td></tr>";        echo "<tr><td><input class="txt_style" id="txt_newPsw" style="font-size:10.5pt; color:#6b6b6b" type="text" name="txt_newPsw" value="new password"></td></tr>";        echo "<tr><td><input class="txt_style" id="txt_reenter" style="font-size:10.5pt; color:#6b6b6b" type="text" name="txt_reenter" value="re-enter new password"></td></tr>";        echo "<tr><td><input class="btn_active" type="submit" name="$btn_active_define" value="$btn_active_text"></td></tr>";

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