I spent some time figuring out the solution today and here it is.
You just need to create a new personal folders, move the stuff that
you want to keep, and close the old personal folders.

Problem:

When you accept a meeting in Outlook, it is putting it into
your Calendar in your Personal Folders instead of the Calendar in
your mailbox on the server.

I have mail filters that move all mail from my server Inbox to an
Inbox in my Personal Folders as soon as it is received.  When I
accept a meeting, it should go into my Calendar on the server.  At
least, that's what it did for the last 18 months.  Suddenly, it
started moving the meetings into the Calendar in my Personal Folders
instead.

Microsoft says:
This behavior can occur because after the .pst file is set as the
default delivery point, Outlook never resets the header information
in the file, even when the .pst file is no longer a delivery point
for messages.

However, there is no way to reset the .pst file to NOT be the
default delivery point.  So you need to create a new personal
folders file and delete the old one.

Solution:

First, check to see if you have the correct
Outlook -> Tools -> Email Accounts ->
View or change existing e-mail accounts ->
should say
Deliver new e-mail to the following location:
Mailbox, your name here

If it says "Personal Folders", then that's why it's putting the
meetings into the calendar in Personal Folders.  Try changing it
to "Mailbox, your name here".  However, I won't be surprised if
that doesn't work.  If it doesn't work, you still need to follow
these directions.

Here is the solution for Outlook 2003.  I assume a similar solution
might work for other versions.

1. First, make a copy of your Personal folders file, just in case.
Mine was located in
D:\Documents and Settings\mylogin\Local Settings\Application Data
\Microsoft\Outlook
and was called Personal Folders.pst.

2. Disable your mail filters.  Tools -> Rules and Alerts -> uncheck
the rules and click OK.

3. Create a new personal folder in Outlook.  Outlook -> Tools ->
Email Accounts -> View or change existing e-mail accounts -> click
New Outlook Data File

4. Move whichever folders you want from your old Personal folder to
your new Personal Folder.  DON'T MOVE THE CALENDAR.  I don't use
the calendar in my Personal Folder, and once it is created, you
can't delete it.  I only want the single calendar on the server
so that it is accessible by everyone checking for my availability.

5. Close the old Personal Folders from Outlook - don't pick the wrong
one!
(right-click, choose "Close Personal Folders"

6. Re-enable your mail filters.  You might need to fix them.

That's it.  This worked for me.

Note that you still have the old Personal Folders .pst file
accessible from Outlook - so you don't need to move all your
Deleted Items, for example.  You can do a File -> Open -> Outlook
Data File to open up the old folders.  (But don't forget to close
them or you will have the calendar problem again.)

There is some useful information in this Microsoft article:
http://support.microsoft.com/kb/293051
However, the steps are for Outlook 2000, PLUS I was afraid to import
the personal folders for fear of pulling in the bad data.

- schneid

Outlook can't make changes on its own.  Why are you moving meeting requests
to the PST?  Change your rule so that it moves only messages and not the
other types of items.