My objective is to install a jar file in a Maven repository. This post explains how to do an install with MVN.
But but since I have Maven embedded in Eclipse, I don\
The default location for the maven repository would be ~/.m2/repository.
Unless you changed this in the preferences of your eclipse plugin, then you should go with that. Replace the ~/ with whatever is appropriate for your home dir on your OS.
Edit: Updating based on the comments: There's an online book available for the m2eclipse plugin, and it would appear that you can run goals from the m2eclipse plugin - see the section here: m2eclipse Goals
I presume there is a wizard of some sort when you click on the goal - I don't have m2eclipse installed here.
Edit2: actually looking at the other answer, this has been answered already :)