Be afraid, be very afraid. There is no telling what the next disaster will be. Another terrorist attack? A steam pipe explosion like the one that shut down several blocks of Lexington Avenue a year ago? Or perhaps a pandemic flu that would cripple New York City's economy by making people afraid to go to work or ride on subways and buses? That was the message at a daylong workshop conducted on Tuesday by the city's health and emergency management agencies, intended to give businesses tips on how to cope with the potential calamities. The workshop had all the portentous, overwrought atmosphere of movies about how the world is coming to an end and everyone had better be ready, from "War of the Worlds' to the latest M. Night Shyamalan film. Only in this faux disaster, the participants