Ugh - that sounds unpleasant.

Do you just need the functionality of a PowerPoint file to be passed around? Or is the need exactly for a PowerPoint file?
MS is making it increasingly hard to work with their stuff outside of their own tools (even more so with the upcoming office from what I have read).

Could you do it with DHTML and or a swf file (which is an open format and therefore allows you to create them without needing the Flash interface)?
Here when we have needed to dynamically work with PowerPoint files, we end up exporting them to DTHML and then soley using it in that format from then on.

But if this is for a client that is demanding specifically that you work with ppt file... ugh, I don't personally know of a way since MS isn't particularly open with their formats.
(although it also depends on how basic you want it to be - from what I have seen in the past when looking on Google, it seems that the eventual response is to use Win32::OLE to then call VB and do it that way... which is... *ugly* - there is also a way to do basic slides - but *not* MS PPT format - if you look here and follow the link in the small print at the bottom)

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There are some odd things afoot now, in the Villa Straylight.