multisession dvd

Hi there, I tried to write a multisession to a dvd. The Problem is, that I cant write the mutisession. I think I´m too stupid to do that :) On every friday the same file will be written to the dvd. I have a script that: 1. tar the files to one file (:o) 2. write an iso with mkisofs (command: mkisofs -R -J -log-file /backup/log/mkisofs.log -o cdbackup.iso /backup/daily/directory/the_tar_file 3. writing the dvd multisession After writing the dvd backup, the dvd will be mounted and the index will be send to my mailbox so I can see if the DVD is full. Could someone give me the right command to write a session to a dvd, or/and which programm I should use. Thanks, Felix