A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
There can be VBA code in PPS files; nothing startling there.
I'm guessing you're opening the file by doubleclicking its icon. Instead, start PowerPoint, do File | Open and browse to the file to open it. This will open it in Normal (editing) view rather than in slide show view.
That'll at least let you look at the slides. And if you want, you can press Alt + F11 to open the visual basic editor and, unless the VBA part is protected, look at the VBA in the project. Sometimes it's just random stuff that someone might have forgotten to remove; other times it could be important to the way the presentation functions.
Also, if you have the 64-bit version of PowerPoint, it may be incompatible with some code from earlier PPT versions; that might also account for the message.