The Bck2Brwsr project is publishing artifact snapshots to Maven repository since Feb 13, 2013. That means there is an easy, three steps, way to start coding for the browser yourself. All you need is Java and Maven installed. Type:
$ mvn archetype:generate -DarchetypeGroupId=org.apidesign.bck2brwsr \ -DarchetypeArtifactId=bck2brwsr-archetype-html-sample -DarchetypeVersion=0.6 \ -DarchetypeRepository=https://maven.java.net/content/repositories/releases/
Maven will download its libraries. Then it asks few questions (for example name of the project you want to create) and generates the skeleton project for you. When the project is successfully created, switch to the created subfolder:
$ cd nameofyourproject
and you are ready to compile and launch your first Bck2Brwsr project:
$ mvn process-classes org.apidesign.bck2brwsr:mojo:0.6:brwsr
Of course, you don't have to work only from command line. Good IDEs, including NetBeans will recognize the generated project without any struggle and provide you all the comfort you are used to when coding in Java.