What do u really wanna do...u wanna convert it from .pps to .ppt or some thing else. If u can conver it into .ppt, then u can do whetever u want........This is what is to be done...
Rather than double clicking on the pps file, go into PowerPoint and then File> Open and then open the file.
As long as it has not been protected you should be able to open and edit it.