One possible idea is to do this with a custom show (I'm not sure if this
will work, but it might). You can put the slides in the order you want them
numbered and then add them to a custom show in any order. You might even be
able to use Side Show > Set Up Show to set the slide show to just play the
custom show. Alternatively, you could hyperlink to the custom show. It might
work. Give it a try.
--David
--
David M. Marcovitz
Author of _Powerful PowerPoint for Educators_
http://www.PowerfulPowerPoint.com/
Microsoft PowerPoint MVP
Associate Professor, Loyola University Maryland
So for your presentation, in Slide Sorter view, you would cut and paste slides 48 and on from your original presentation ("presentation A") to a separate blank presentation ("presentation B"), and set the slide number of presentation B to start at page 48.
Then, you'd have to use David's method to hyperlink from slide 47 (or whatever the last slide is of presentation of presentation A to the first slide (now renumbered to start with the number 48) of presentation B.
The custom show thing that David mentioned might work too.
Is it important that the actual slide numbers change, or just the displayed page numbers?
Although this would be troublesome with longer presentations, you could just manually add slide numbers to the slides as you like. I wouldn't recommend this if you're making lots of changes, though.
Alternatively, you could let PowerPoint automatically number your slides via the Slide Master, but then have slides 48 and on stop displaying the slide number by changing the slide layout. So, slides 1-47 would be auto-numbered, but slides 48 and on would be numbered manually.
Basically put, there's no easy way to do this with PPT 2008 for Mac.
Jeff