Create files in that directory you are not supposed to, as far as I understand the 'proc' filesystem. 'proc' fs is to let you read messages from the kernel and to send commands to the kernel with those virtual files (they don't phisicaly exist in your HD).
But for a guru to help you here, you need to provide some more info. What are you trying to write in that dir ?
Also there is some documentation at : http://www.linuxforum.com/linux-acpi.php
 Had wrong URL pointing to specification of acpi implementation >.<