How to create a .ICS file with multiple VEVENTs to be imported into an existing Outlook Calendar

I don't think this will work. Outlook is limited in importing those "open" specs. I had a similar problem trying to import a vCard file with multiple contacts. I ended up splitting the file and writing a script in Outlook to import all the files in a directory.

This is possible, using an Internet Calendar (like from Google). Outlook 2007 has the capabilities to subscribe to an Internet Calendar (under Account Settings) and Outlook 2003 has an open-source plug-in available. You could create an accessible feed that is "read-only". The format is like

BEGIN:VCALENDAR  
PRODID:-//XYZ Corp//My Product//EN  
VERSION:2.0  
CALSCALE:GREGORIAN  
METHOD:PUBLISH  
X-WR-CALNAME:My Calendar  
X-WR-TIMEZONE:(GMT-05:00) Eastern Time (US & Canada)  
BEGIN:VEVENT  
DTSTART:20061021T100000Z  
DTEND:20061021T130000Z  
DTSTAMP:20090211T175526Z  
UID:5f98dfd5-ac72-4ae1-b3c2-799a4e7c91f9  
CLASS:PUBLIC  
CREATED:20071104T183833Z  
DESCRIPTION: My description text.  
LAST-MODIFIED:20071104T183833Z  
LOCATION: 123 Anywhere Street\; Anyplace, NJ 12345\; US  
SEQUENCE:0  
STATUS:CONFIRMED  
SUMMARY: My summary text.  
TRANSP:OPAQUE  
END:VEVENT  
BEGIN:VEVENT  
DTSTART:20061101T170000Z  
DTEND:20061101T180000Z  
DTSTAMP:20090211T175526Z  
UID:6eaef015-eb90-4e94-8e6c-0003b928969a  
CLASS:PUBLIC  
CREATED:20071104T183833Z  
DESCRIPTION: My description for number 2.  
LAST-MODIFIED:20071104T183833Z  
LOCATION: 123 Anywhere Street\; Anyplace, NJ 12345\; US  
SEQUENCE:0  
STATUS:CONFIRMED  
SUMMARY: My summary for #2.  
TRANSP:OPAQUE  
END:VEVENT  
END:VCALENDAR

Make sure you are using a unique UID for every VEVENT. If you use the same UID for every VEVENT you would see exactly the behavior you are describing since only unique UID's are processed and added to the calendar.

HTH.