Thanks for that acrylian.
Yeah, I don't know much php at all. I've had a look through that first link and it shows:
function imageNumber( ) {
in the template-functions.php file. Is that what I'm supposed to be editing?
I had a look through http://www.zenphoto.org/news/how-to-read-the-zenphoto-functions-guide but I have no parameters for this function, so if I am supposed to be editing that particular bit of code, I'm not sure what I'm supposed to be changing. Also, in the first link you posted, it says 'int' so I'm assuming it should look something like:
function imageNumber( [int $?? = ?? ) {
Again, I've got no idea, so I could be way off (and probably am).
Any help appreciated.