Outlook PST folders missing after upgrade

[Dave]

I had the 2nd level subfolders within my PST file
disappear after upgrading from Outlook 2000 to Outlook
2002.

First I uninstalled Office 2000 and installed Office XP.
When I started Outlook 2002 and added the PST file into
Outlook, some of the contents of the folder were missing.
I then uninstalled Outlook 2002 and reinstalled Outlook
2000. When I imported the PST file, the folders were
still missing.

Ex:
+ Personal Folder
+ From John
+ From Pat
Inbox
+ Japan
Travel
Unknown
(any folders that should have been under from john, from
pat, japan, etc. are all missing)

Is there any reason this may be happening?