I doubt many "techno composers" use notes. The best program for you would probably be something like Cakewalk Sonar or Steinberg Cubase, but they're both very expensive. And there is Propellerhead Reason which I'm sure is very popular among composers of electronic music, but it's more technical/oldschool with actual simulations of cables dragged between different virtual machines, like synthesizers, filters etc. It doesn't feature notes, but it has a piano roll editor (i.e. you see a virtual piano keyboard on the side (vertically), and bars represent notes ( the longer bars, the longer notes).
If you're just looking to make some more or less simple techno music just for fun you could go for some kind of "tracker", like Modplug tracker, for free. Wikipedia has an article about trackers: http://en.wikipedia.org/wiki/Tracker
Trackers are inherently suitable for composing techno music. The concept is that you have a matrix with one column for each sound channel, and you input notes using the keyboard. Notes are represent like "C-4" or something like that in the matrix, the number being the octave. Of course, you need sound samples for them.