You'll need to use the
cvswrappersfile provided in the devtools. The easiest thing to do is to copy it to your homedir and prepend a dot:
% cp /Developer/Tools/cvswrappers ~/.cvswrappers
You can also add the contents of that fike to your repository.
.pbprojfiles aren't handled by the cvswrappers by default. You'll need to add a line like this:*.pbproj -k 'b' -f '/Developer/Tools/cvs-unwrap %s' -t '/Developer/Tools/cvs-wrap %s %s' -m 'COPY'