To initially checkout a copy of plex86 from the CVS repository.   Note that the use of -z3 (use gzip compression during transmission) is optional.

cvs -z3 co plex86

To update your local copy of plex86 with modifications which developers have made, change directory into the main plex86 directory and:

cvs -z3 update -Pd
For more information on usage of CVS, check out the CVS documentation at SourceForge.   Look under Resources -> Site Docs.