First make sure that that code has been committed. The code tagged by this command is the last committed one, not including uncommitted changes in the current tree.
Change to the project root folder and issue the following command:
cvs tag [tagname]
cvs tag R0_3_3
Note that the tag format must contain no spaces or dots, and must begin with a non-numerical character.
Now the tagged code can be checked out:
cvs checkout -r [tagname] [module]
NOTE: The tagged code cannot be changed. To change tagged code that are not head of branch, use branch.