1. Close Minecraft
  2.  
  3. Press Start
  4. Type: %appdata%/.minecraft/bin
  5.  
  6. Copy minecraft.jar to a safe location.
  7.  
  8. Right-click the original and select open-archive (or similar) under WinRAR.
  9. Right-click MineFly.zip and open it the same way.
  10.  
  11. From MineFly.zip
  12. The mods folder in Appdata to the .minecraft folder.
  13.  
  14. See all of those .class files in the other folder? Transfer those to mincraft.jar
  15.  
  16. Open Minecraft again. If it doesn't work delete minecraft.jar and copy the backup to the original location.