User-916962509 posted
Do you mean ppt (presentation)? PPS is a "Powerpoint show" and I'm unfamiliar with that. PPT seems a lot more popular.
The old ppt format is binary based, whereas the new pptx format (Office 2007) is purely XML based, so once you work out how the PPTX is built, you can just build some XML in the right structure and save it as PPTX... Job done.
Some information here:
http://openxmldeveloper.org/forums/thread/2311.aspx
However, you will need a viewer to open PPSX from Office versions lower than 2007, but IIRC Microsoft provide this for free.
Good luck
bgs264