Download the PPLANE java file using the following link: pplane.jar. Save the file in a place where you can find it (e.g. your Desktop).
To run this, you will need to have Java installed on your machine. This is probably the case, but if not then go to http://www.java.com , from where you can both check whether you have Java (and whether your Java is up to date) and download Java. Be careful during the installation of Java: the install might try to change your web homepage and search engine to Yahoo!
You should then be able to run PPLANE by double-clicking on the pplane.jar file you downloaded. Your computer might complain about running code from an unknown developer. You will need to give the necessary approval to run the program: this might involve bringing up your security preferences.
PPLANE was developed by John C. Polking, who is at the Department of Mathematics, Rice University. Here is a link to his PPLANE page (page currently not working), which has more information, including terms and conditions for using his software (free to use at educational institutions).