Other's like spreadsheets need to be completely in RAM (or simulated RAM), or all the calculations may not work.
Power Points could fall either way, or probably more in between. They are mostly sequential when being displayed, but tend to need to be all there when being edited. A smart program could switch things in and out of RAM as needed. I don't know if Keynote is that smart.
At any rate, I remember another poster who had a 1.5 GB Power Point that he definitely could not get to run in Keynote. So, I don't know if 1GB will work or not. The only way to find out, since no one seems to know actual specs, it to try it and see.