Kevin, at WizBang, is fielding tech questions about Windows XP. There’s some amount of discussion already about the idiosyncrasies of Outlook XP and how it manages large *.pst files (uh, if you don’t know this already, the *.pst file is your mailbox and all its contents; lose that and you’ve lost it all!).
My two cents added to the kitty is this: If you want a reliable way to backup and restore large *.pst files, then use OutBack Plus, from AJ Systems. It’s a robust backup program that can backup your *.pst files to any drive, including a removable drive. I can’t live without it! Read some reviews of it below: