<body ....>
...
<form ....>
....
<textarea name='content' id='content'>Some existing text area content put here</textarea>
<script type='text/javascript'>
var oFCKeditor = new FCKeditor('content');
oFCKeditor.BasePath = \"fckeditor/\";
oFCKeditor.Height = '500';
oFCKeditor.ReplaceTextarea();
</script>
Note:
1. assumes that your fckeditor scripts is in fckeditor subdirectory to the current page.
2. textarea element name is "content", hence FCKeditor is also named "content"