inserthtml - how?

I've got a fckeditor that is initialized with this code:

var oFCKeditor = new FCKeditor( 'serendipity[body]' ) ;
oFCKeditor.Config[ "AutoDetectLanguage" ] = false ;
oFCKeditor.BasePath = '/blogs/fckeditor/' ;
oFCKeditor.ReplaceTextarea() ;

My question is how to use the inserthtml function with this.

FCK.InsertHtml('test'); doesn't seem to work.