Frank,
Giradman has an imaginative approach above. I'm impressed with his insight and effort. I suspect, however, that the coordination of the slides and video may turn out to be a major challenge, assuming that's a requirement. The iPad's multitasking capabilities are limited at best. And the tools to create the kind of content you're looking for, while impressive for the iPad's limited processing power, are inherently limited.
So if you hit a roadblock, as I suspect you might, you may want to consider another approach, altogether. For example, if the central requirement is the display of the combined content on the iPad (rather than its creation there) you may want to consider an app like LogMeIn or Splashtop that would enable you (or your client) to run the slideshow/video content on a PC or Mac and simply display it on the iPad. That, of course, assumes an internet connection to the host system but if that's not a dealbreaker, it may be a more direct route to meeting the client's needs.