it is possible the other way around!
simply save your PPT as PDF (there are many free PDF 'printers') and upload that. this should work just fine, unless you have videos in your PPT.
if you do have videos, you would need to upload them separately in FLV format...
we will simplify all this in the future of course
and look into how to create prezi that can be embedded into ppt
you can probably link the exe from ppt, but of course that will change windows, etc, not so smooth