I have from time to time had to address various DCOM errors in MOSS.
There are several good blog postings out there and I am primarily writing this note to help remind myself and tell others about them.
For the DCOM errors related to launching the object with CLSID {61738644-F196-11D0-9953-00C04FD919C1} with event id 10016 check out this article:
http://soerennielsen.wordpress.com/2007/04/16/fixing-those-pesky-dcom-event-log-error-10016-in-a-sharepoint-farm-environment/
For the DCOM errors related to the search services and caused by the MSFT October hotfix check out this article:
http://share-point.blogspot.com/2007/11/mosswssv3-bug-in-sharepoint-public.html