Xml insertBefore problem

1

I have a xml file with structure like this:
<root>
<images>
<name>xxxxxxxx</name>
<thumb>zzzz</thumb>
<caption>ttttt</caption>
</images>
<images>
<name>yyyyyyyyy</name>
<thumb>uuuuuu</thumb>
<caption>oooooo</caption>
</images>
.
.
</root>

the xml is created in flash, now when I try to modify it, say call out a particular set of <images />, I remove the node first, then create a new one, then when I try to insert it back to the xml, this is what happened:

i = 10;
var insertPoint = my_xml.firstChild.childNodes*;
var newNode = new XML ( new node details here );
my_xml.insertBefore (newNode, insertPoint);

result:
<root>
<images>all the nodes in between as per normal</images>
</root>

<images>
<name>new name</name>
<thumb>new thumb</thumb>
<caption>new caption</caption>
</images>

// this set is supposed to be “inserted” to a insertpoint and before </root>, but it is now outside <root>, can any one help?

thanks heaps