Photoshop is a photo editing program. It's very much overkill if you just want to run a slide show. Photoshop's real utility is as a digital dark room, and you may find it useful for altering and enhancing your images, but there are plenty of other programs that will display them in a slide show just fine, and for basic cropping/enhacing, etc., Photoshop is still overkill.

Powerpoint is the name of a Microsoft product that is designed for giving presentations. It allows you to incorporate photos and graphics, but is mainly focused on text and slide layout. It too is overkill if you just want to display a series of photos.

What you need is a simple photo organizer with a slideshow function, of which there are dozens of decent free (or inexpensive) programs. Apple's iPhoto (for Mac only) or Google's Picasa (for Windows only) should fit the bill. Both are free. Those programs are focused on organizing your pictures, not on editing them (although they do include some basic, easy-to-use editing features).

If you find those programs insufficient for your needs, Adobe also sells a couple of stripped-down versions of Photoshop that would do what you want. Photoshop Album is $50 retail and Photoshop Elements is $100. Both are probably available for discoutns, or bundled with many scanners.

But my guess is that iPhoto or Picasa will do the trick just fine.

One thing I recommend is having your existing slides professionally scanned by someone with a good slide scanner. The cheap flatbed scanners out there that come with slide-scanning adapters can't compete with the quality you get from a professional-grade slide scanner. Once you've scanned your slides, you can take future photos with a digital camera and you won't have to worry about scanning yourself.