Create a branch from within a sandbox

cvs tag -b branchname [filenames]

Create a branch from anywhere using a tag name or revision

cvs rtag -r [tagname|revision]
-b branchname project

Create a branch from anywhere using a date or time

cvs rtag -D [date|time] branchname project

Check out a branch sandbox

cvs checkout -r branchname  
project

Convert an existing sandbox to a branch sandbox

cvs update -r branchname [filenames]