The best sources of information are Developing Ant Plugins for Maven 2.x and Maven: The Definitive Guide: Chapter 11 Writing Plugins.
Each ant script requires two files, which have to be named following the conventions for ant plugins:
So if you want to add a new foo-bar ant script you would create a foo-bar.build.xml ant script file and foo-bar.mojos.xml mapping document.
Both these files should be located in the src/main/scripts directory.
If you want to access variables from the component's pom.xml in the ant script then you need to do two things in the mapping document:
This plugin uses commons as the goal prefix. So if you add a new foo-bar goal, then it can be executed on the command line using mvn commons:foo-bar. This prefix is defined in this plugin's pom.xml.
Not alot to say about this except, if you need access to additional variables from the component's pom.xml in the ant build script then you will need to define additional parameters for these in the associated mapping document.