You have two options to install the application on your mobile phone: downloading the .jar file, then installing it on the phone or downloading it directly to the phone (Over-The-Air).
If you are interested in experimenting or modifying the midlet, you can download the Java source code as well.
The two files you need are available here:
(as far as I know, only the .jar file is used for installation)
Just point your phone browser to http://www.bonnefon.org/files/PokerTimer.jad and the last version will automatically be installed.
The source code is available here