I have written a Windows service that spawns a separate process. This process creates a COM object. If the service runs under the 'Local System' account everything works fine, but if the service runs under the 'Network Service' account, the external process starts up but it fails to create the COM object. The error returned from the COM object creation is not a standard COM error (I think it's specific to the COM object being created).

So, how do I determine how the two accounts, 'Local System' and 'Network Service' differ? These built-in accounts seem very mysterious and nobody seems to know much about them.