okay, thanks everyone, I've found it.
Up until yesterday, all I had ever seen were the 3 files of the free Star Wars screensaver (alx and cod files) and couldn't figure out how to add my own images to that.
Yesterday I found and downloaded the full screensaved_0.5.4 project, and have since added my own photos, compiled, copied .cod over the existing .cod, installed on my BB device - easy once you know how!
The full screensaved_0.5.4 project has a link here in Blackberry Forums:
Pics
Michael.