How to Practice Vipassana?
A hammer has two ends for a reason; one end is great for pounding nails, but not at taking them out. The nose is avoided in Vipassana for a reason; it is too apt to lead to calm.

That being said, it is of course technically possible to cultivate insight at the nose, if you insist. Vipassana takes as its base the four elements, earth, air, water, and fire. As per the Visuddhimagga:


  But one whose vehicle is pure insight, or that same aforesaid one whose vehicle
  is serenity, discerns the four elements in brief or in detail in one of the various ways given in the chapter on the definition of the four elements.
  
  -- Path of Purification XVIII.5


So, you have to find the elements at the nose; there is some faint pressure, which is the air element, and there is heat and cold, which is the fire element. The breath itself is a concept, so you can't use that as an object of Vipassana. You might note "hot, hot" or "cold, cold" or "hot, cold", as it presents itself. Also, "feeling, feeling" for the pressure. 

Having taken that as a base, you would then note whatever other experiences arose, based on the four foundations of mindfulness, as per the instruction given by a teacher.

And, what Anthony said :)