how do you change the order of slides in a slideshow?

If you are in the slideshow view just drag the pictures to the location that you want them to show in.

Super fast resolution per Tiffany of Apple Support (Thanks, Tiffany!) - it's a bug in the Slideshow Button featured at the bottom of Albums and Events windows. You will need to create an actual slideshow, as follows:

Select the images you want to use --> chose "Add To" --> "Slideshow"--> "New" or chose an existing slideshow.

You will be able to manipulate your slideshow options (theme, music, order, etc) from there.

I tried "building" the slide show one slide at a time beginning with the one I want first, then second, and so on. I have the photos sorted in order of title in the album. Creating a slideshow with the photos in the album loses the sort order. So I tried dropping just the first 10 photos into the slideshow and tried to reorder the photos and the photos seem to just jump around. I cannot get the photo order to stay. Any suggestions?

You're posting in an old thread and no one is saying what version of iPhoto they have. But the usual cause for this is the slideshow template you use, as iPhoto tries to fit the images into the appropriate running order based on aspect ratio of the images to fit the template.