The ONLY difference is in the associated documentation.
The Documentation for MSIB2.5 covers Windows 2003 also.

>-----Original Message-----
>Is there actually any differences between msib2.1 and
>msib2.5? I know that the msib2.5 package includes extra
>bits like CS SP2, sharepoint stuff and updated
>documentation (support for Win2k3) but is the code
>actually any different. To install it you run the
>msib2.1.exe package then the setup.exe file when it has
>been extracted from the former. The setup.exe,
msib21.pup
>and msib21.sdo all appear to be the same version in both
>2.1 and 2.5.
>
>Reason for the question is that we have developed some
of
>our site on 'msib2.5' (Win2K3) and need to deploy it to
>production which is 'msib2.1'(Win2K3). Do we need to
>upgrade our production site to 'msib2.5'?
>.
>

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