When your calendar is finished, embedded in a web page, and ready to view, it will not appear to be a read only file. It sems like any visitor can edit and modify the page. That's probably because you are viewing it on the machine and/or log-in in which you created it. Your calendar will appear to be modifiable by site visitors. It isn't. For any visitor on his or her own log in or machine, the site will run exactly as you wanted it to. Have faith. Try it.