If you do want a slide show with images and video, import it all into iPhoto and run the slideshow from there.
But what if you just want to create a slide show, no transitions, no titles, no fuss, no faff?
What if this slideshow can contain all sorts of visual media, images of course, but also PDFs, text documents but ... not video. Well not yet.
So, you have a folder stuffed full of the slide show content, (including content in sub folders) how does this magic work?
Easy, open Preview if it isn't open already - Grab the folder and drop it on the Preview icon in the dock.
Or, if you're drag and drop dysfunctional, go to Open, and browse to the folder you want to use, just click on the folder (not its contents) and click open.
Now all you do is choose View > Slide Show from the main menu.
If you have got something you want to include in the slideshow that Preview does not like, eg, an Excel spreadsheet - just 'print' it and save it as a PDF. Sorted.
To loop a slideshow, and include video.
Dump all the media (video/image/pdf) in one folder (no sub folders)
Select it all, and press the spacebar to launch Quickview
Then go to full screen and press play.
Finally, make sure any media you want to use for a presentation is on your local hard drive (on your computer), not on a shared drive, unless you like the spinning beach ball of death that is.
Keynote simplicityIf you really want to use Keynote, this can be quite painless as well—not as quick as the methods outlined above, but maybe only few minutes longer...
Just select all the media (including PDFs, but it will only display the first page) and drag and drop it into the navigation panel on the site. Keynote will place each separate item on it's own slide, it will resize large images to fit, but smaller images will be left at original size.