Grant's advice is correct from my experience. The biggest amount of hassle was clearing my bike through customs in Santiago. Chilean customs officials are very "thorough" and there are several forms that must be signed by one official, carried to another building, signed by another official, and brought back to the first building. My shipping company provided an agent that made the process pretty painless, though time consuming. In all it took about 6 hours (including the afternoon siesta) to clear customs in Santiago (actually Valparaiso since my bike arrived by sea).
I did not travel with a Carnet or motor vehicle insurance and they were never asked for in Chile or Argentina. Border crossings between Chile and Argentina usually took less than an hour for both sides. I usually had to show my motorcycle registration, title, and passport - that was it. I don't remember that anyone ever even asked me for my driver's license, though I suggest that you carry an international driver's license.
You should find the customs and border crossings to be pretty painless. In fact, you may find (as I did) that much of the time at many border crossings is spent talking to the officials about where you are from and where you are going!