Download the current Java SDK including NetBeans from Oracle's Java page and install it. Test now whether the Java plugin for your browser is installed by looking at an applet page, e.g. the mathematical pendulum. If necessary download and install the plugin.
Finally create an arbitrary directory for all your PhysBeans activities, e.g. C:\physbeans, and copy the latest PhysBeans library physbeans.jar from the download page into it. Now start NetBeans and immediately exit again. This will create the directories for the user-specific part of the NetBeans configuration. You will find them at C:\Documents and Settings\YOUR_USERNAME\Application Data\NetBeans\7.2\config.1
Now proceed with the configuration of NetBeans.
1 Depending on your Windows version they can be somewhere else. To locate them use the directory search of Windows and look for .netbeans.