Don't waste your time adding a target="_blank" attribute in your sitemapNode, IT DOESN'T WORK. There is a work around though. Add JavaScript to open your link in a new page.
Example:
(Will not work)<sitemapnode url="http://www.google.com" title="Google" target="_blank">
(WORKS!)<sitemapnode href="javascript:var w=window.open('http://www.google.com','google');" title="Google" />
