You should put the unscrambler in the directory the wii file is in. Then open Notepad and type "unscramble pi-nfsc.wii pi-nfsc.iso" and save it as a .bat file. Put that .bat file in the same directory as the unscrambler and wii file are and execute the bat file.
Try the unscrambler the comes integrated with Rawdump 2.0. Have not tried it yet but it looks like you no longer need any command line stuff. Try it out.