You'll need to create the slideshow then upload it 'as a movie'. I suggest you use windows movie maker which is a free download (if not already installed on your machine) and very easy to use, or Photostroy - ditto, free and simple, but with nice copyright-free incidental music effects.
With either of these you add in your photos, add in any text you want, then finish the movie - then this finished item is what you would upload into Youtube.



