The Maven Source Plugin creates a JAR containing the sources of a project and attaches it to the main artifact of the project.
It would be nice if you could directly use this JAR as source attachment for a bundle in your Eclipse target platform, but Eclipse 3.4 expects a special Source Bundle format with specific headers in the manifest. There is a feature request to support this directly in the Maven Source Plugin.
To fill this gap, I had a look at the sources of the Maven Source and Archiver plugins and wrote my own maven-sourcebundle-plugin. This plugin is available for public use as a subproject of the DataScript project hosted at BerliOS.
There is no public Maven repository for this project yet, but it is contained in the latest binary release rds-bin-0.30, or you can get the sources from Subversion.