I do not really this this is a practical proposition. I do not think that pps files actually contain graphic information, but a database of instructions to direct Powerpoint what to do on screen. I really think that you probably need an embedded PC with a suitable graphics subsystem. One of course could just connect a laptop to a projector, but you are obviously not wanting to do this. I might point out that I am making a general assumption here, and someone may indeed say it is possible. I would say though, that this is rather unlikely. Good luck anyway.
Added after 9 minutes:
Just a further thought. Perhaps you gould get a micro ATX board and install windows and powerpoint, then have it boot up in pp. You could then set the input file as a usb device. I dont use pp, but I would have thought you could get it to load up the last file used, when it boots. If you then make sure that the file on the memory stick always has the same name, whatever it contains. Well its an idea anyway!