DataNucleus can be easily developed using Maven, Eclipse, or other IDEs (let us know if you write docs for how to develop DataNucleus with a different IDE). You require JDK1.6+, a Git client (to download/commit DataNucleus Git-based projects) and an editor. DataNucleus is split into several plugin projects and you may need these building in a particular order due to dependencies.
All DataNucleus plugins are Maven projects, with a pom.xml. To build and install the plugin simply type
mvn clean install
and the plugin is built and installed in your local Maven repository. If you are developing some feature that requires updates to, for example core (datanucleus-core), an api (e.g datanucleus-api-jdo) and a datastore (e.g datanucleus-rdbms) then you will need to build these in the same order, core first, then the API, then the datastore.
When building/developing using Eclipse the first thing you need to do is install the Eclipse "m2e" plugin (if not already done). This means that the build of any plugin will build using Maven (and get its dependencies from Maven). You also should import the eclipse-build repository. This provides a complete set of third-party dependencies that are then "exported" for use by all other Eclipse projects (the DataNucleus plugins). It is hoped to drop this step at some point in the near future as many plugins no longer require it. You then need to import all DataNucleus projects you are working on (as well as any dependents, such as datanucleus-core).