Select the Left Shoulder, and go to the properties dialog. If you've got one of the more recent Beta versions, your job will be fairly simple. Otherwise, things are a little (but not much) more difficult.
If you see a tab
on the Properties dialog that says 'Hierarchy', select it. You will
see scaling boxes. Click in the 'X' scaling box, and type '-100'.
Instantly, the bone structure should flip around the X axis, to position
itself on the left arm.
If you don't see such a tab, you'll have to do it by hand. Go into the properties of each bone. You will see a Start Position and End position box. Click in the 'X' box and set it to the opposite value. Note that for attached child bones (like the Forearm) the start position may already have been set when you get there: because the bone is attached to its parent, setting the End position of the Bicep will cause the start position of the forearm to be automatically changed.
Once you have the bone structures properly copied, you will need to
attach control points to them as you did on the right arm. Then you'll
be ready to deal with the legs.