I get the same message with Outlook 2003 as well.  It happened in Outlook 98. I have searched everywhere to find that file, but I can't seem to get it.  Anyone out there know what to do to at least get the annoying message off everytime I start Outlook.  It doesn't appear to hurt the functionality of the program, but it is highly annoying

The add-in "C:\Windows\System32\ActExt.dll" could not be
installed or loaded...

I resolved the issue of getting the error message every time you open Outlook 2003.  The problem is that the file Actext.dll apparently causes outlook to function improperly, so it must be disabled.  To get the error message from appearing every time I open Outlook I did the following

I found the file Actext.dll on google.com at a website that specializes in dll files.  I downloaded the file to C:\Windows\system32\actext.dl

Then I opened Outlook.  A message popped up, and said that this particular file causes problems, and asked me if I would like to disable the file.  Click Yes, to disable the file.  After that, you should not get the message anymore. At least it worked for me

By the way, the solution proposed by Microsoft at http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q820671 does not work for Outlook 2003, and it incorrectly identifies the file as an ACT! file, when in fact it is a Norton file
   
    ----- anonymous@discussions.microsoft.com wrote: ----
   
    I upgraded to OfficePro recently, and now I am getting
    the following message when I as the Outlook program loads
   
    The add-in "C:\Windows\System32\ActExt.dll" could not be
    installed or loaded...
   
    The message goes on to suggest using the Detect and
    Repair function, but this does not clear up the problem
   
    Any ideas
   
    Thanks