Note that you must use pax if you need to extract the tars.
The files in the tarfile is stored with absolute paths, so you need to strip the leading / if you want to extract the files (otherwise it will try to extract the files to /cvs... )
do this to extract the files to a directory cvsbkp/ pax -rv -f thetarfile.tar -s "/\/cvs\/data\//cvsbkp\//g"

2 Source code

 #!/bin/ksh
 #
 # More scripts and tips can be found at
 # http://www.edlin.org/
 #
 # Script to generate BACKUPS of a part of the CVS repository (dilbert is the cvs server)
 #
 
 _ftp_file()
 {
   stty -echo
   read -r PASSWORD?"Enter password for user $2 : "
   stty echo
   print
 
   #$1 = server
   #$2 = userid
   #$3 = source
   #$4 = targetdirectory
 
   #extract filename
   filename="`expr "//$3" : '.*/\([^/]*\)'`"
 
   ftp -in $1 <<EOF
     user $2 $PASSWORD
     bin
     get $3 $4${filename}
     quit
 EOF
 }
 
 echo "Script to generate BACKUPS of a part of the CVS repository"
 echo "----------------------------------------------------------"
 echo "This script will make a tarfile of the files at dilbert:/cvs/data/theFiles"
 echo "it will save the tar-file in the directory \"bkps\", so make sure that directory exists"
 echo "NOTE: The files are stored with ABSOLUTE paths in the tarfile, so you need"
 echo "to use pax to extract the files somewhere else"
 
 filename="cvs_theFilesbackup_`date +"%Y_%m_%d_%H%M"`.tar"
 
 echo "Logging in to server to create the tarfile..."
 #Note: you might need to login as soem other user to be able to read the data in /cvs/data/
 #it depends on how your cvs is set up
 rexec dilbert -l ${USER} "tar cf /tmp/${filename} /cvs/data/theFiles"
 
 echo "FTP the tar file over to this server..."
 _ftp_file "dilbert" "${USER}" "/tmp/${filename}" "/home/${USER}/bkps/"
 
 echo "Logging in to server to delete the tarfile..."
 rexec dilbert -l ${USER} "rm /tmp/${filename}"
 
 gzip /home/${USER}/bkps/${filename}