These are instructions to build Selena EAP Maven Integration, the support for Maven2.
svn checkout http://svn.jetbrains.org/idea/Trunk/maven idea-maven-integration
mvn install assembly:assembly
That one should build the whole Selena EAP Maven Integration plugin distribution. Make sure you are online when building for the first time, it will download multiple IDEA API artifacts.
In the target directory you will find a ZIP archive of the distribution maven-integration-VERSION.zip.
Now unzip the archive into your Selena EAP plugin folder and restart IDEA.
Make sure to delete or move the existing Selena EAP Maven Integration plugin located at $SELENA_EAP_HOME/plugins/maven. Otherwise this can interfere with the new one you just created.