This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
By definition, a MODAL window is supposed to prevent the user from using other windows until they are finished interacting with the modal window. Why would you want to usurp that? If you don't want it to be modal, don't use a modal window. You probably need to rethink your user experience design if you feel you really need to open another window from a modal window.