Ok so basically you have two different scripts that are going to be put together.
The login script can be found at Hotscripts.com under user php/user authentication or you can use this url:
http://www.hotscripts.com/PHP/Script..._direction=des
and then a file upload script which can be found also on hotscripts.com or you can make your own through this tutorial:
http://w3schools.com/php/php_file_upload.asp
If you need any help combining them let me know, and if you do, be sure to tell me what user authentication script you will be using.