Then you need to make your presentation on a PC, I have seen strange issues of powerpoint screwing up with simple user interface elements from PC to Mac powerpoint so it isn't perfect.
The only way to guarantee your presentation will work is to bring your own laptop/cables, Macs can export to DVI, VGA or S-Video so should be able to work with any projector and then you can use Keynote.
guarantee? wow...i'm an audio/video technician that specializes in computer support for corporate conferences and i've seen plenty of times where a person's laptop takes a dump in the middle of the presentation. they forgot to charge the battery, they didn't bring their power cord, they put the system to sleep after a short period of time, their video card doesn't like being attached to a projector, their video card isn't robust enough to play the video on the local screen and the projector, they forgot the adaptor for dvi to vga, yadda yadda yadda.....
one of the companies i work for typically requires presenters to submit their presentations to a centralized "speaker ready room" beforehand. it's then run off of our machines in the meeting room; desktop machines with robust video cards, fast hard drives, and plenty of ram. and we have a backup machine in the meeting room. in many cases we have macs in the room as well but for those times when we don't we convert it over to a pc and most of the time it's without too many hiccups. when a problem does occur we fix it.
mac to pc powerpoints do indeed have their issues from time to time. most of the time it is because the mac user doesn't run the office compatibility check to see what will work on the pc side of things. most often they used tiffs instead of jpgs or they relied heavily on transparencies or used fonts not available on the pc system.
now that being said, every last one of these issues can be dealt with if you have a mac to work on. export the tiffs to jpgs, you can export entire slides to jpgs or pngs and then reimport the images, if the slide has animations you can import it multiple times and rebuild it by cropping to the various elements you want to appear or disappear. so on, and so on.
i'm personally looking forward to office 2008 to see if it is more compatible between mac and pc. it would solve a lot of my "busy" work and free me up to take care of other things.