What distro are you using? I'm running Fedora 13 on my Studio 1537, and the brightness worked out of the box for me. Are you having actual issues, or are you just trying to find where it would be located? Do the following to see if you have this file or not:
If it says unsupported, then that's not the right file. I need your input though of what distro you use so I can track the file down for you.