how do I set an alarm for an appointment

CC Calendar does not have an alarms function built into it.

One way to create alarms, however, is to write a script that looks for appointments happening in the next 30 min. (For instance) Then use the Events Plugin or ScriptFire to run this script every 30 minutes. (The Events plugin lets you run a script at a certain time, or every X minutes, among other things.) Only works when FileMaker is running, of course, but it can be pretty cool.

Rather than run this on every workstation, you can set up an "agent" machine with the Events Plugin on it and have it email people about upcoming events. If you don't want to use email, you can employ the Troi Activator plugin (that does need to be on each workstation) to let you run scripts on a user's compute by IP address. This effectively lets the agent call a script on someone else's machine to show a dialog or otherwise alert them to the alarm.

Of course you can also use this agent machine to run other, automated routines like printing reports, performing ODBC synchronizations, etc. You'll wonder how you lived without one!