Thanks for your reply. Actually the Lightroom help Overlay procedure is what I have been trying and it doesn't work for me. (the overlay text shows on all slides in the slideshow not just a single slide. Even when I follow the procedure for a single slide.) My keystrokes are > Slideshow>ABC>Custom Text Popup>Edit>IPTC>Caption> "actual text for caption" . The caption still overlays on every slide in the slideshow. What am I doing wrong ?
Please remove the caption or Title from all the images apart from the one you want to keep.
Then click on ABC and choose Caption or Title. It will add the caption automatically from the metadata. All the other images will be showing a field written "<Empty>"
Please refer the video : The Slideshow Module « Julieanne Kost's Blog
Let me know if this helps