These are screenshots of Apple's FileMerge utility. 

If you have any questions about them, please ask me
(fitz@red-bean.com).

FileMerge1.jpg
- This is what filemerge looks like when you launch it without any files.
        
FileMerge2.jpg
- Ready to compare two files

FileMerge3.jpg
- Comparing files (note the arrows... you can click on them, then
  change them around).

FileMerge4.jpg
- Comparing files

FileMerge5.jpg
- Deciding which file(s) to choose.