Hi KurtOne thing about I-stock is that they specifically prohibit using their photos for screensavers. You can pay extra and get an extended license, I think that is what it is called, but then your pictures cost something like $50 a piece which if you have alternating pictures would be rather expensive.
I have been looking for some place that allows you to use the photos in screen savers and so far haven't found one. (Most have fine print that says you cannot.) If anyone knows somewhere that does allow screensavers I would be happy to know.