also make sure you are aware of the directions of both the x or y direction, and the surface normal, because that will affect how the sketch is oriented
I don't remember much about NX3, but in NX6,
Click on the sketch in the model tree, then "copy" (right mouse button), and then simply use the "paste" command (under "edit") and then follow the dialog instructions.
It will probably take a few tries to get it right.