Power Point files, be it marked as .PPT, PPTX or with any other compatible extension out there, may be created, edited and viewed using online services.

That version should open your moldy (sorry: aged) PowerPoint files, then let you save them in Office 97 format. From there, you should be able to open them in PowerPoint 2007.

Learn how to convert and open Apple Keynote file in PowerPoint on Windows computer using Keynote tool or Zamzar and Cloudconvert online web apps.

Ankush khandelwal asked about compatibility issues between files created in different versions of Microsoft Office--specifically the big changes in file format that came with Office 2007.