Do a search for some different possibilities, but one is that in PPT you can save the slides as jpegs (or PNG...I forget) probably from File - Save As.
Converting a Powerpoint to video as we speak - it was a presentation so i shot the speaker with 2 cameras, then had a seperate camera hooked (via rca cables) from my AverKey Imirco ($99) display converter.
Basically - take computer vga output from laptop, plug it into converter box, then run a vga cable from converter box out to the LCD projecter ( basically a bypass).. converter box then has option of RCA output or S-video to any recording device, tv ect..
Works nice for capturing the transitions most ppt presenations have
Powerpoint doesn't like to export selected pictures as a picture file. :( But, Openoffice.org does (it's an opensource office program). I just did it. I'd recomend d/l that program & trying that one.