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What is with the really crappy post on one super-long line for your
entire post?  Whatever NNTP (network news transfer protocol) client
you use is crap.  It should be physically wrapping line so they are
under 70 to 76 characters in length each.

From your headers:
   Organization: Outlook Forum
   User-Agent: FUDforum 2.7.5RC2

Oh, I see from your headers that you really posted in FUDforum, not to
Usenet.  It appears that the forum operates a forum-to-Usenet gateway
to pretend it has a larger membership than it really has.  That is,
they *lie* about who are the real members in just their own forum by
pretending Usenet is part of their forum.  Tell your forum admin that
their gateway sucks.  Posts gatewayed to Usenet should not consist of
just one really long line.

Don't post using a forum-to-Usenet gatewayed community.  If you want
to post to Usenet then come here instead of the misconfigured forum.
Use a real newsreader client, like Outlook Express.  For Microsoft
newsgroups, you can connect your newsreader to msnews.microsoft.com
(if you don't want to use the one provided, if available, from your
own ISP).

Regarding your problem:

Did you use auto-archiving in Outlook so the old items are in a
different .pst file?

Rather than import from whatever .pst file you believe is your backup,
use File -> Open to open it as a separate message store in Outlook
(rather than trying to merge it into your new message store).  Then
you can see just what is in that old .pst file versus what got
imported.  If you find there are more items in the old message store
when opened separately in Outlook then you should be able to drag them
from the old message store to whatever folders you want in the new
message store.