You need to have Java (at least 1.1.8), Swing and javacomm installed on your machine. These can be downloaded from the IBM site.
A screen size of 800x600 or larger is strongly recommended.
The latest production and test versions are not available for OS/2 because the build machine we were using is no longer available.
See the Download pages for v1.2.5, the last production version that supported OS/2.
Unzip the file you downloaded above. This will create the "JMRI" folder.
To install, you just have to move the JMRI folder to where you want it on your computer.
You can run the program by using the "DecoderPro.CMD", "PanelPro.CMD" or "JmriDemo.CMD" scripts in the JMRI folder.