I personally would use this solution as the emails are not writable any more and what happens during the next arcive session? Another CD then another then another.
I would store the PST files locally say PST2002, PST2003, PST2004, PSt2005 or PSTCompanyA-m, PSTCompanyN-Z or something.
then either store these on a server drive and control backup centrally or if you are determined to use CD get the user to back them up every x weeks and send reminders to everyone every so often too. The year method will not change so that is suitable for CD backup but the company method is not as these will always be growing.
Think security tho, whats the easiest way for me to steal HR confidential emails? Go into the HR dept and take the cd off the desk.
Any help?
Iain