Here's a couple options for you.
1. Free remotely hosted
http://server.com/siteapps/calendarapp/
2. A script with a decent free version that I believe will do what you want, plus it has an active support forum.
http://www.calendarix.com/
If free doesn't work out, CxCalendar Lite is a powerful script at $19.
http://www.caliberx.com/