The new window script step can open a new window and if the next script step is go to layout, the two steps in combination will open a new window with the size and position you specify with the layout you select.
But if you are on a windows system with windows maximized, additional code is needed to manage the size of the original window.
Also, New Window gained some new options in FileMaker 12 not available in older versions. One option makes the new window "modal" meaning that users cannot interact with the original window until they close the new floating window. There are ways to use a script to get this same effect in older versions of FileMaker.
If any of these details are issues you need to deal with, let me know.