maven-archetype packaging is available since 2.0-alpha-1: it should be used instead of jar, which was used for Archetype 1.x.
Using maven-archetype packaging helps identifying archetypes in repositories and adds archetype related bindings to build lifecycle: see maven-archetype packaging documentation for more information.
The server id used to download the artifact is [archetypeArtifactId]-repo: you have to define corresponding server configuration in settings.xml with this id.