You need to add a new repository to your repositories in maven. If you look in the pom.xml file in the directory where you are typing mvn, you may find a list of repositories, possibly in a default build profile. You need to copy one of them, and replace the data.
The repository where your pom that you are missing is here (maybe): https://svn.apache.org/repos/asf/geronimo/server/trunk/framework/buildsupport/car-maven-plugin/
Now, that is the location of the pom, the repository, you might want to cut it back to ../server/trunk
for the description and name, just make something up. make sure that you set snapshots to true and releases to false. I can't really give you much more information, but if you read the quickstart guide to maven (here: http://maven.apache.org/guides/getting-started/index.html ), you will find what you need, with the exception that maven might not know how to use the directory structure of this source code repository, I'm not sure, but it doesn't have a directory structure which matches the package names, such as org.apache.geronimo.car-maven-
plugin, there is 'framework' and org.apache is back in the svn.apache.org.
I hope that what I have written will help.