First install a Java runtime or Java development environment (J2SE). This can be obtained from Sun's Java sites . It is recommended to use version 1.4 or above.
For using plb4jedit, you need to install jEdit (download from http://www.jedit.org). An installed PL/B compiler makes sense to compile PL/B sources. The quickstart guide for the installation of jEdit may help.
Then download plb4jedit binary distribution and unzip into your $HOME/.jedit directory. Restart jEdit. Done.