AFAIK, an Iframe cannot be used that way. You need to point its src attribute to another page.
Here's how to get its body content using plane old javascript. This works with both IE and Firefox.
function getFrameContents(){
var iFrame = document.getElementById('id_description_iframe');
var iFrameBody;
if ( iFrame.contentDocument )
{ // FF
iFrameBody = iFrame.contentDocument.getElementsByTagName('body')[0];
}
else if ( iFrame.contentWindow )
{ // IE
iFrameBody = iFrame.contentWindow.document.getElementsByTagName('body')[0];
}
alert(iFrameBody.innerHTML);
}