yup.. I have to deal with Powerpoint alot these days (the company I work for gets them from speakers etc and they have to be made into PDFs for printing etc) some people make 40mb powerpoint files which is crazy!
If you do get involved, take you hourly rate x by the number of slides then double it for the hassle the job will become.
Most importantly agree, before you start, the cost of changes. Obviously if you've made a mistake then you can't charge, but if your client decides to change their mind after you've finished, you don't want to be doing it all again for nothing.
Ugh I'm in the middle of a powerpoint job, think it's going to be 60-80 slides in total, that's a hell of a long presentation! Do find it an utter pain to work with and often find myself designing elements in illustrator and just importing them as jpegs as to set them up in powerpoint would take an age.
Sound advice on charging by the hour, as some slides will take seconds others 30- 40 mins.
I know that many designers charge their clients by the hour. Well I am no agree, cos we all know that you can put how many hours you want , so in this way we can loos our credibility. I think the best way to charge for designing a website or in this case a power-point presentation, by the number of pages created and complexy of that website ..