There are several things that can make OE very slow to start. Try these
suggestions one at a time. Note about extracting files: if you have Win98,
click Start|Run and type without quotes "sfc", then use the Extract button.

1) Restore the file "Imagehlp.dll" in your Windows/System directory.
 extract win98_32.cab /a [filename]
 (on some systems, it is found in win98_26.cab)
 (for IE5 users on Win95/NT, it is found in setup295.cab)

2) Try replacing the following 4 files in \windows\system:
 psbase.dll, pstorec.dll, pstorerc.dll and pstores.exe.

   To do so, first close Outlook Express and any IE windows. Next, copy
   the 4 files to a temporary folder so that you can restore them if
   needed. Now find the Windows Update Setup Files directory which
   contains the CAB files for IE5.  Extract the 4 files using the
   following command:
 extract ie_s1.cab /a [filename]
 (on some systems, it is found in ie_s4.cab)

   When all 4 are extracted, copy them to the \windows\system directory,
   choosing to overwrite the existing files if you are prompted. Then
   reboot the computer.

3) Compact your OE files by clicking File|Folder|Compact All Folders.
   If that doesn't help, close Outlook Express and rename or delete
   the file "folders.dbx". Close  first. By  deleting this file, OE5
   will rescan your Store Root folder to create a new index of all
   messages, folders and subscribed newsgroups. It will destroy all
   nesting of mail folders (hierarchy), as well as remove all lists of
   newsgroups on all news accounts. Your subscribed newsgroups will
   remain, however you will have to reconfigure their synchronization
   settings.

FYI, #1 is associated with installing McAfee anti-virus after installing OE.
The McAfee install deletes the Imagehlp file by mistake. If
you restart the computer after uninstalling an older McAfee and before
installing an update, the problem does not occur.

#2 can occur if a program was running in the background at the time
that you installed OE5. Anti-virus apps are the most common ones to be
running. That prevents system files from being updated by the install.

#3 helps for those who upgraded over an existing OE4, and especially if
the OE4 folders had not been compacted before the upgrade.

--
Tom Koch  (MS MVP)