Steve,

I was recently interested in doing something similar. Take a look at the code below.

I'm still working on a class to test this so when I have 100% coverage I will update.

trigger test_custom_calendar on Testable__c (after insert, after update) {
	//new list of events
	list<Event> ev = new list<Event>();
	
	
	for(Testable__c t : trigger.new){
		//if new record, populate these fields
		if(trigger.isInsert){
			Event e = new Event();
			
			e.StartDateTime = t.Start_Time__c;
			e.EndDateTime = t.End_Time__c;
			e.Agent__c = t.Agents__c;
			e.OwnerId = UserInfo.getUserId();
			e.WhatId = t.Id;
			e.default_invitee_one__c = 'Peter Tosh';
			e.default_invitee_two__c = 'Gregory Isaacs';
			//add new rows
			ev.add(e); 
		}
		//if parent is updated, delete original event and create new
		if(trigger.isUpdate){
			Event dead_events = [SELECT WhatId, StartDateTime, EndDateTime FROM Event WHERE WhatId IN : trigger.old];
			delete dead_events;
			
			Event e = new Event();
			e.StartDateTime = t.Start_Time__c;
			e.EndDateTime = t.End_Time__c;
			e.Agent__c = t.Agents__c;
			e.OwnerId = UserInfo.getUserId();
			e.WhatId = t.Id;
			e.default_invitee_one__c = 'Peter Tosh';
			e.default_invitee_two__c = 'Gregory Isaacs';
			//add new rows
			ev.add(e); 
		}
	} 
	//insert new list
	insert ev;
}

-Natty