I think Microcontainer jar used in Seam comes from Embedded project, which I believe is currently unbuildable. :-(
But running Maven in Microcontainer is the same as running Maven elsewhere - simply go to Microcontainer's root directory and run 'mvn install'.
You should then get target directory in every module's directory. Simply pick up those artifacts that you need + check 3rd party lib dependencies and get them from your local Maven repo (should be there, since they will be picked up during build).
In the future we are planning on having different build configurations to join all the artifacts that you need - e.g. jbossas config, standalone config, minimal, ...
One problem I got into was a number of dependencies were NOT marked as "optional" and there seems to be a whole ton of dependencies that get tossed into any MC-dependent project.
Is this getting straightened out?
Having MC beta4 out, a lot of the issues was solved.
But the fact is, that MC is not a small project, so pulling out large number of dependant libs is not that surprising.