Custome batch rename

Good Afternoon

My photographic club use Bridge. We would like to be able to batch edit image names in order to make a random slideshow. The filename format is "123 Sunny Day", i.e membership number space image title. We'd like to be able to have the 123 replaced with a 3 digit sequence number 001, 002 etc. I saw a solution on the net and tried it but it didn't work - I can't seem to find the right formula so any help appreciated please.