I don't know about Win XP
On the Mac, you have three choices for keyboard layout:
-Persian
-Persian ISIRI 2901
-Persian-QWERTY
All of them have it on Shift+Space. There is no need for shortcut.
Since the keyboard output on the Mac is application independent (for the large part) most shortcuts will be applied to any application. For creating a shortcut for something the keyboard layout does not provide, you can go to:
System Preferences > Keyboard & Mouse > Keyboard Shortcuts
You can then click on the plus sign (+) to create a new output for a shortcut. If that key or key combination is already taken for another task, the system warns you to relocate one of duplicates.
-b