You must install Python before installing OpenRTM-aist. You need to install the 32-bit version of Python when installing the 32-bit version of OpenRTM-aist, and install the 64-bit version of Python when installing the 64-bit version of OpenRTM-aist.
Download and install the installer from the link below, OpenRTM-aist-1.2.x-RELEASE_x86_64.msi for the 64-bit version, and OpenRTM-aist-1.2.x-RELEASE_x86.msi for the 32-bit version.