Mirroring depends on what type of modeling method you're using (all can be found in Maya's help files):

If you're using polys: Polygons >Mirror geometry

If you're using sub-d: Subdiv Surfaces > Mirror

With NURBS, just duplicate the object and scale along the axis the original object lies on in an equal amount. For example, if I drew a curve and revolved it around the z-axis and it's 1 in z-axis (in the channel box). Duplicate the revolved item, and scale it to -1 in the z-axis to mirror it.

As far as the other question goes. Take a look at Kevin's "skellington" tutorial (skeleton) and try to apply that to your simple man shape. Otherwise, fork out the $22 for membership and download some of the vip tuts...the mech is easy enough and has a modeling and rigging movie.