A Java SDK usually is included in Linux distributions. Simply use the standard software installation program of your distribution to install a current version (1.5 or later). The installation usually includes the plugin that is necessary to run the Java applets in the browser. Test it now by looking at an applet page, e.g. the mathematical pendulum. If that doesn't work you probably have installed an older Java version and have to integrate the plugin manually. Details depend on your distribution.
Next install NetBeans 7.2 or later. If it is not provided with your distribution you can download it at the NetBeans homepage.
Finally create an arbitrary directory for all your PhysBeans
activities, e.g.
/physbeans, and copy the latest PhysBeans
library physbeans.jar from
the download
page into it. Now start NetBeans - using the proper menu oder
startup tool of your environment or directly from the shell
with /opt/netbeans-7.2/bin/netbeans & - and immediately
exit again. This will create the directories for the user-specific
part of the NetBeans configuration. You will find them
at /.netbeans/7.2/config.
Now proceed with the configuration of NetBeans.