If you are able to save your Powerpoint files as some version that is compatible with use in the Microsoft Explorer browser, you could try using the Web Tracker item type that would allow for MediaLab to record the links that participants click while viewing the files. Otherwise, my earlier recommendation of use of the Custom item is the best best for you to use html code to present Powerpoint files while also defining specific responses for participants to click on options as well as advance to different slides.