You can get the latest CVS distributions from Cyclic Software [2]; they also sell professional support for CVS. CVS Bubbles [3] by Pascal Molli has links to other resources.
The CVS Manual [4] by Per Cederqvist is the definitive reference, is well readable and includes a good introduction. It is available in
PDF,
HTML and
Windows Help formats. For beginners that want to start quickly, the CVS tutorial [5] by Jim Blandy is worth reading. Brian Berliner put together a paper on the
theoretical background of CVS CVS II: Parallelizing Software Development [6].