Under no circumstances delete any PST file without checking it's date
modified attribute.
This monolithic file "Outlook.pst" IS your data/folders inside of your
outlook, and it won't break until it reaches 1.83 GIGS.
This file is the single file that contains ALL messages you've received and
sent, as well as your contacts and calendering items!
Sometimes when outlook is slow, find and RENAME (NEVER delete until you've
tested) *.DAT files you find in your outlook folder.
Extend.dat to Extend.old
Outllib.dll to Outllib.old
Outcmd.dat to Outcmd.old
(source:
http://support.microsoft.com/default.aspx?scid=kb;en-us;325370)
And perhaps an OUTLPRN (no extension) file if you find them.
Once renamed, run some restarts, reboots, and test. YOU WILL LOSE
CUSTOMIZATIONS to toolbars and the like, but the basic files rebuild where
the renamed (corrupted?) ones were and you can recustomize.
THEN, when you feel safe, delete the *.OLD files.
Ken