请教Fckeditor加载问题

如下代码，为什么在document的ready事件中就报FCKeditorAPI未定义的错误，而下面按钮的点击事件就没有这个问题？我现在有些和FCKeditor有关的操作希望能在页面加载的时候执行，所以肯定不能等到点按钮，所以请教此问题是否能解决？或者在其他的事件中解决？
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <script src="static/js/jquery-1.4.1.js" type="text/javascript"></script></head>
<body>
    <form id="form1" runat="server">
    <div>
        <div>
            <input name="fckContent" type="hidden" id="fckContent" runat="server" />
            <input type="hidden" id="fckContent___Config" value="" />
            <iframe id="fckContent___Frame" name="fckContent___Frame" src="FCKeditor/editor/fckeditor.html?InstanceName=fckContent&amp;Toolbar=cms"
                width="700px" height="360px" frameborder="no" scrolling="no"></iframe>
        </div>
        <div>
            <input id="Button1" type="button" value="button" onclick="return Button1_onclick()" />
        </div>
    </div>
    </form>
    <script language="javascript" type="text/javascript">
// <![CDATA[
        $(document).ready(function () {
            var oEditor = FCKeditorAPI.GetInstance('fckContent');
            var str = oEditor.GetXHTML();
            alert(str);
        });        function Button1_onclick() {
            var oEditor = FCKeditorAPI.GetInstance('fckContent');
            var str = oEditor.GetXHTML();
            alert(str);
        }// ]]>
    </script>
</body>
</html>