Use the lock command to lock the current revisions.
When performing this command and your user account does not have admin privileges in the repository, you will get an error message like this: cvs [admin aborted]: usage is restricted to repository administrators In this case, ask your CVS administrator to enable admin privileges for you.
If you are the CVS administrator, do folloging (taken from CVSNT documentation): In the CVSROOT directory on the CVS server, create a file named admin, which, is not checked into CVS. Each line in this file contains the user name of each user account with admin privileges. If SystemAuth=no (CVSROOT/config file), the names are those that appear in the passwd file.