This is not an easy task, and the path to such a downgrade would be fraught with the possibility of error. It is not recommended. I also believe that it is not necessary as any MapReduce code you write for 1.1.2 will most likely run on 1.0.4 and vice versa. The main differences between these version of hadoop are bug fixes. The easiest method of getting a hadoop 1.04 installation would be to follow our manual install instructions on a single node.