How to ‘git commit’ a single file/directory

Your arguments are in the wrong order. Try git commit -m 'my notes' path/to/my/file.ext, or if you want to be more explicit, git commit -m 'my notes' -- path/to/my/file.ext.

Incidentally, Git v1.5.2.1 is 4.5 years old. You may want to update to a newer version (1.7.8.3 is the current release).