Unfortunately, pps is not a video codec. It's a file format. You can not import it into Premiere Elements.
The best compromise is to export each page of your PowerPoint presentation as a JPEG and then import each into a Premiere Elements slideshow.
I say "best compromise" because the quality of JPEGs produced by PowerPoint is usually not very good.
You might be better off recreating the presentation in Premiere Elements from scratch.
As Steve points out, this is a PowerPoint Project file, and is only usable in either PowerPoint, or a PowerPoint player.
Now, this article in the PrPro-Wiki, might be of use to you. It is written for PrPro, but will apply to PrE.