For starters see Pascal's nice document at:
https://openacs.org/new-file-storage/download/cvs.html?version_id=140
A useful tip: You can see the difference between the repository and your copy without altering your copy using "cvs -n update". (The "-n" switch means "do nothing".) Also, even if cvs update overwrites your locally modified files, it saves a copy of your file with ".#" prepended to the filename. Pascal, can you update your document with this information?
There is an explanation of what the update output flags mean (e.g. P, M, C, etc) somewhere. I usually check the info file in emacs.