[cvsnt] switch a branch in readonly

[Nathalie]

I am running a CVSNT 2.0.58.0 on a windows2000 CVS repository.

When there is a compilation and livraison version, I create a new 
branch. Can I switch a branch in readonly on a server (the developers
can checkout this branch only for read, only the head branch can be 
modify) ?

I try
      cvs admin -l[branchname] but it doesn't work.

Thanks for your help !