Backing up Outlook2000

Oulook has been backed up on this XP system by using the Export Wizard. The .pst file was then imported into another pc (win98)into Outlook 2000 and lo and behold the various folders resotred ok together with their contents but + additional messagesetc which had been deleted from the original source. The owner of the two units wants to be able to do a weekly backup of his Outlook data onto a CD-RW but does not want a load of duplicate content. I witnessed his procedure and can confirm that he had definitely deleted all but most recent stuff and cleared “Deleted Items”

Any ideas?