• use File::Find to get an array of the file names.
• Then you can use a regex to separate the file names into their constituent parts. eg
  my($words,$fix_num,$remainder)= $filename=~ /(.*?)(\s\d+)(\s-\s\d{3}\.jpg)/;
• sprintf will then allow you to specify the padding on $fix_num
• Then rename the files with rename

Have a go at doing this and come back with your code if you have any problems ;)