ACPI support in linux and debian is improving but it is not as simple or easy as the other commerical OS. Below you will find links to more information on ACPI.
http://www.columbia.edu/~ariel/acpi/acpi_howto.0.2c.html - Up to date documentation (Oct 2005). [Url not working]
http://www.lesswatts.org/projects/acpi/ - A page created by Intel developers working on patching the kernel to improve ACPI support.
http://www.tldp.org/HOWTO/ACPI-HOWTO/ - Some older info.
In Debian Synaptic Package Manager you can search on ACPI and get a list of tools that help you monitor and initiate.