Here is something you should look at
Improve PowerPoint's GIF, BMP, PNG, JPG export resolution
http://www.pptfaq.com/FAQ00052.htm

Signature
Michael Koerner
MS MVP - PowerPoint
>I am trying to export power point slides as jpegs on a PC at 72 dpi and the
> default setting seems to be 96 dpi. Does anyone know how I can change
> this
> so that I can export jpegs on a PC for use on a Mac at 72 dpi? Thanks!
Sabrina - 31 Oct 2006 00:43 GMT
Thank you, actually in between the time that I posted and your response I had
stumbled upon this. It did EXACTLY what i needed, thanks so much!
> Here is something you should look at
> Improve PowerPoint's GIF, BMP, PNG, JPG export resolution
[quoted text clipped - 4 lines]
> > this
> > so that I can export jpegs on a PC for use on a Mac at 72 dpi? Thanks!
Michael Koerner - 31 Oct 2006 14:29 GMT
Glad we could help, and thanks for getting back to us with your success.

Signature
Michael Koerner
MS MVP - PowerPoint
> Thank you, actually in between the time that I posted and your response I
> had
[quoted text clipped - 9 lines]
>> > this
>> > so that I can export jpegs on a PC for use on a Mac at 72 dpi? Thanks!