Retrieve a node value containing html tags


through server side script I built this html output:

<content><a target='_blank' href='#'><img title='' alt='' border=0 src='image/image.gif'></a><span></span></content>

I want to append the content of <content> to a new div but
doing this in javascript:

var html_link = banner.getElementsByTagName("content")[0].firstChild.nodeValue;

I obtain in the alert box:
html_link = null

where is the problem? How can I assign to var html_link the content of <content>?
can you help me please?

many thanks