This applies ONLY to Exchange 2000 and not Exchange 5.5 (which could
not be modified without PSS) - how can you change the contents of the
following Exchange system generated warning sent to users that are
over their mailbox quota:

<B>Subject:</b> Your mailbox is over its size limit
<B>Body:</B> Your mailbox has exceeded one or more size limits set by
your administrator.
Your mailbox size is xxxxxx KB.
Mailbox size limits:
	You will receive a warning when your mailbox reaches 81920 KB.You may
not be able to send or receive new mail until you reduce your mailbox
size.
To make more space available, delete any items that you are no longer
using or move them to your personal folder file (.pst).
Items in all of your mailbox folders including the Deleted Items and
Sent Items folders count against your size limit.
You must empty the Deleted Items folder after deleting items or the
space will not be freed.
See client Help for more information.

If it is not possible, please list the reference where this was
obtained from.

It appears that this oft requested feature is still not available for
Exchange 2000.There is no setting in Exchange 2000 that you can change
to be able to edit this message.
No information on how to change this message is available in the
Exchange 2000 docs on MSDN .
      MSDN : Exchange 2000
     (http://msdn.microsoft.com/library/default.asp?url=/nhp/default.asp?contentid=28000408
)

However, if you are upto some hardcore dll hacking, then there may be
a solution.
This message is hard coded into an Exchange 2000 DLL file mdbsz.dll.
You can edit this file using the Rlquiked tool which is available as
part of the MS Resource Localization Toolset.
         MS Resource Localization Toolset 
         ( ftp://ftp.microsoft.com/softlib/mslfiles/rltools.exe )
Please note that modifying this file will probably make your
installation unsupported and if done incorrectly, may even corrupt the
dll file.So I wouldn't recommend this unless you really know what you
are doing.

List Of Google Groups Discussions on this subject :
   - microsoft.public.exchange2000.admin
     Sub : Database size limit message
     ( http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=uGC1H2JuBHA.2528%40tkmsftngp03&rnum=9&prev=/groups%3Fq%3Dmdbsz.dll%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN%26tab%3Dwg
)

   -  microsoft.public.exchange2000.admin
      Sub : Custom message
      ( http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=uon9riSgCHA.1816%40tkmsftngp12&rnum=8&prev=/groups%3Fq%3Dmdbsz.dll%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN%26tab%3Dwg
)

   - microsoft.public.exchange2000.admin
     Sub : How "Mailbox Size Warning Message" modified?
     ( http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&threadm=ul07hdmeCHA.2668%40tkmsftngp10&rnum=7&prev=/groups%3Fq%3Dmdbsz.dll%26hl%3Den%26lr%3D%26ie%3DUTF-8%26sa%3DN%26tab%3Dwg
)

 - Google  Group Search Terms : mdbsz.dll
  (http://groups.google.com/groups?q=mdbsz.dll&hl=en&lr=&ie=UTF-8&sa=N&tab=wg
)


=============
Hope this helped.
If you need any clarifications. just ask!
:)

I looked for 30 minutes and didn't find anything.  Great answer and
exactly what I was looking for.