Apparently the "Window" menu cannot be accessed directly by scripts. The following code return a null script object:
Object objMB = GetMenuBar();
Object objWindowMenu = objMB.FindMenuItemByName("Window");
OKDialog( "\"Window\" menu object is valid?\n\n" + \
(objWindowMenu.ScriptObjectIsValid()? "Yes" : "No") );
What I'm trying to do is to install my script as menu item under "Windows" menu and at the position before the "Floating Windows" sub menu.
Is there a way to work around this?
No there isn't. Menu entries from the core application will always sit on top.