Mars Installer cannot detect what Windows version you're using.
But you can create a different .ini files for each Windows version.
I'm gonna think about detecting Windows version and using appropriate .ini file for the next release but now you must do it manually.
This program is made to be started from Windows installation (GuiRunOnce, cmdlines.txt) so depending on Windows you're installing you can run appropriate .ini file. If you're running it from already installed Windows - there is no way do run appropriate .ini (x86 or x64 for example).
Is there any life on Mars ?