To be able to do this you will need to have the following info:
Domino Server Name where mail file resides
mail file name on the OS.
Whith that info all you do is create a calendar document in the mail file with all the necessary fields populated. You can read the IBM RedBook COM Together for help on the COM interface and accessing the database. There are a few examples that you can download with the RedBook. Here is hte URL to download the PDF version of the book and if you click on the link called Aditional Material to download the samples.
IBM Redbooks | COM Together – with Domino
Hope this helps