To do this, click Save As., select Other Formats, then TIFF Tag Image File Format.
Using PowerPoint 2007, I was able to save the presentation as a TIFF file. When I went back to my work, I found my own solution. I'm running into this sort of dead end on the Net more and more these days.
After reading the replies posted, I just gave up. I had the same question as you did and surfed into this site looking for a simple answer.