Would the Windows screensaver do the trick? You can set it to display a folder of photos, which transitions are used and at what interval the pics are cycled, etc.
I use the photo viewer in Nero 9, but that's not free and might be an expensive way to go about it if all you want is a slide show viewer
FastStone have a free picture viewer that may serve your purpose, however, with slide show, customisable transition effects and background music if so desired.
