I received this in response to a question to IBM on possible solutions.
I did not know that MS had published this.  It applies to OUTLOOK 2000.
We are currently working with MS on getting this to work with OUTLOOK
2003.  Currently in our environment OUTLOOK 2003 NEVER lets go of the
.pst files.  I believe that is a bug......   This procedure does work
with OUTLOOK 2000 in our shop.
Matt
 
The *.pst file is locked by Outlook while it is used
   continues to be locked for 30 minutes (by default) of inactivity.    
   There is to configure to release the lock earlier than 30 minutes    
   of activity, which could give a chance to TSM to backup the file.    
   I would recommend that you take a look at a Microsoft article which  
   discusses this issue. This is Microsoft KB Article 222328, titled    
  "OL2000: (CW) How to Change File LockTimeout Value for PST Inactivity"
   which can be found on the Microsoft support website at               
    http://support.microsoft.com/default.aspx?scid=fh;EN-US;KBHOWTO     
.