You could try,

1) Select the first curve
2) duplicate and move to the desired location
3) Right click [vertex] on the new curve, select the end vertex and hold down 'V'
4) with V held down move the vertex of curve 2 towards the end of curve 1. It should snap the vertex to the exact location of the first vertex of curve 1.

Repeat steps 3,4 for the other end of curve 2

'x', 'v, 'c' (and maybe others) perform 'snap to' commands when moving on object/edge/vertex.

x snap to grid
v snap to vertex
c snap to curve

hope that helps

:edit:

The you can attach the curves or whatever if you need them to be seen as a single object etc