Instead of going all the way to the folder where the minecraft.jar should be replaced, just put the minecraft.jar file in the same folder with the program (or put them both in the desktop) and run the program.

The program will close itself automatically after it will move the .jar file, it moves it almost instantly.
Make sure the file called minecraft.jar - otherwise the program won't move it.

This program is very simple - one row code of a batch file. (If you want to see the source open it with notepad, notepad++ or any other text editing program..)

IMPORTANT: Read the ReadMe.txt file first!!!
(otherwise you won't be able to run the program!)