The install-file goal is used to install artifacts to the local repository.
The example below shows how to install NUnit 2.2.8.0 into your local repository.
mvn npanday.plugin:maven-install-plugin:install-file
-Dfile=../imports/nunit-2.0/nunit.framework.dll
-DpomFile=../imports/nunit-2.0/pom.xml
-DgroupId=NUnit
-DartifactId=NUnit.Framework
-Dpackaging=library
-DartifactVersion=2.2.8.0