I searched in the Sonatype repository and svn , but I also did not find the jar or sources. Custom lifecycle mapping is an experimental feature in m2eclipse. Therefore, if you do not need this feature, you can comment on this plugin.
Edit
After some tests, I noticed that if you use Maven 3.0 Embedded runtime, your pom will work without complaint, but there is no jar for this plugin in the repository yet. So there is some magic or I need to know more about Maven3 / Embedded :)
alt text http://img683.imageshack.us/img683/7041/m2eclipse.png
source share