I assume it's the JSPTabContainer you want to use, so it's a horizontal tab (by default).
What should happend to the original desktop when you open the new window ?
The only solution I can think of currently is to manipulate the tabs.jsp in such a way that you for example look for the tab name and instead of the link to "original" tab content you insert your link to the external page or call a javacode snipplet which itself opens an new window and refers to the new content.
/u