Speaker objectt (sound triggering) and NLA editor


I would like to use the NLA editor with sound strips to trigger sounds emitted by some speakers. I use the 2.68a version of Blender.
My problem is that I have not “add sound” menu item in the NLA editor even if the corresponding sound strip is selected. I watched one tutorial but my version of Blender seems not behave like the one in the tutorial.
Thank you for any help