Reader Bill has a number of really old (circa 1991) PowerPoint files that he wants to open in Office 2007. Unfortunately, Microsoft neglected to include support for the "really old" format in its latest version of PowerPoint, so Bill's stuck.
I have a couple suggestions, but to be honest, I'm not positive any of them will work. Thus, I'm going to open this up to you, the real geniuses. If you know of a way to open or batch-convert old PowerPoint files, hit the comments and share your wisdom. In the meantime:
Idea #1: You might be able to "step" your way to Office 2007, meaning using an older version of PowerPoint to migrate files to the newest version.
For example, you could probably pick up Office 97 Small Business Edition for cheap on eBay or Craigslist. 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. (Here's where I claim ignorance: Does that version even support Office 97 files?)
Idea #2: Microsoft has a Registry hack designed to let PowerPoint 2003 SP3 open older PowerPoint files. It's possible that same hack will work for PowerPoint 2007. If you're willing and able to try it (I would, but I don't have any old PPT files lying around for testing), leave a comment telling me how it went.
Idea #3: You could try online file converter Zamzar, which supports a pretty healthy number of formats.
Well, that's it, I'm out. I hope one of these solutuions works for you, Bill, but I think the more likely outcome is that an uber-smart reader will come up with something better.