Yes there is : use the Win32::OLE methods and have a look at the Outlook Object Model and from there you should be able to figure it out...
You can navigate through the items part and check to see whether it's actually a calendar...

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Edited 1:38 PM 8/15/03
To have a look at the Outlook Object Model, you can use VB's editor included in Outlook by pressing Alt+F11 and then once it's opened, you can use the library (press F2). It's got all you need and is very useful.
You can also have a look at the MSDN...