Microsoft Corp. is promoting its free online service for storing files and collaborating on projects as a way for teachers to keep classes on track even if schools close because of a flu outbreak. Microsoft has launched a how-to Web site that walks teachers through the steps of setting up accounts for their classes on Office Live Workspace, a free Web service. Teachers can use it to post handouts and presentations, and students can log on to get assignments, chat and work with classmates on shared files.