http://www.phpdeveloper.org/view_tut.php?id=41
The above is just an example of one. The thing is, user login/authentication scripts can vary from system to system which will all depend on what it is that you need.
Therefore, just providing you files will do you NO good unless you are capable of modifying the code to fit your need. OR, you hire someone to write one for your system.
As someone has already said before, it is essential that you learn some PHP if you plan on doing this yourself.
Good luck!