It's controlled by the user, though they may not realize it. See
http://www.rdpslides.com/pptfaq/FAQ00189.htm

Signature
Sonia Coleman
Microsoft PowerPoint MVP Team
Autorun Software, Templates and Tutorials
http://www.soniacoleman.com
> PowerPoint 2003 ppt files open as a PPS when launched via a link on our
> Intranet. We were told that this was a security setting with XP
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>
> Joe