Most FrontPage users just pick up another script from a 3rd party such as www.hotscripts.com and then use that with FrontPage. Depending what server you are on, hotscripts should have a variety of calendar scripts to work from. They won't work inside frontpage as an "add-on" but you can still use them.
I keep recommending this one but I like it and the one-calendar version is free. Check out Brown Bear Software. It can even update your Outlook calendar.