I got it!!! So, actually the fallowing lines is what i`m looking for:

my $root = $doc->getDocumentElement();
my $whole_node = $doc->createElement("url");
$whole_node->setAttribute("id","14");
$whole_node->setAttribute("link","http://www.yahoo.com");
$whole_node->setAttribute("name","The first link I ever saw");
$root->appendChild( $whole_node );
[download]

Right now the problem is that in the xml file the text is not so well formated :( (is this a real problem?) What do you thing this is the right solution, or there is a simple way to add comtent to that xml file?