Thank you for your post.
A New Windows script step will open a new window. If you want a specific Layout, then you'll need to specify it in the script step Go to Layout. If you specify just Go to Layout, it will go the Layout. It will not create a new tab nor a new window.
Please note that this in context of Instant Web Publishing, IWP. Carolyn has indicated in another thread that she can't get the new window to open in IWP even though the new window step is shown as "compatible".
What is meant by a "virtual window" anyway?
New Window in Instant Web Publishing will not create a new web window. It will keep the original window in order to stay connected to FileMaker Pro via the browser. There is an internal pointer knowing the location of the original window. When you issue Close Window, the original window returns (within the same web window).