ACPI in Linux hasn't matured to the point it's at in Windows. It might not work at all on your box. I have quite a few different motherboards, and it only works reasonably well on one laptop.
Issue "cat /path/to/kernel/.config | grep -i acpi" to show your options. On the box here where I have stuff under /proc/acpi/ I'll show you the output.
Code:
mingdao@titus:~$ cat /etc/slackware-version
Slackware 10.2.0
mingdao@titus:~$ uname -a
Linux titus 2.6.16.22 #1 PREEMPT Fri Jun 30 20:26:09 CST 2006 i686 pentium4 i386 GNU/Linux
mingdao@titus:~$ cat kernel/linux-2.6.16.22/.config | grep -i acpi
# Power management options (ACPI, APM)
# ACPI (Advanced Configuration and Power Interface) Support
CONFIG_ACPI=y
# CONFIG_ACPI_SLEEP is not set
CONFIG_ACPI_AC=y
CONFIG_ACPI_BATTERY=y
# CONFIG_ACPI_BUTTON is not set
CONFIG_ACPI_VIDEO=y
# CONFIG_ACPI_HOTKEY is not set
CONFIG_ACPI_FAN=y
CONFIG_ACPI_PROCESSOR=y
CONFIG_ACPI_THERMAL=y
# CONFIG_ACPI_ASUS is not set
# CONFIG_ACPI_IBM is not set
# CONFIG_ACPI_TOSHIBA is not set
# CONFIG_ACPI_CUSTOM_DSDT is not set
CONFIG_ACPI_BLACKLIST_YEAR=0
# CONFIG_ACPI_DEBUG is not set
CONFIG_ACPI_EC=y
CONFIG_ACPI_POWER=y
CONFIG_ACPI_SYSTEM=y
# CONFIG_ACPI_CONTAINER is not set
CONFIG_X86_ACPI_CPUFREQ=m
# CONFIG_X86_ACPI_CPUFREQ_PROC_INTF is not set
# CONFIG_PNPACPI is not set
mingdao@titus:~$ ls -lh /proc/acpi/
total 0
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 ac_adapter/
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 battery/
-r-------- 1 root root 0 2006-07-04 22:15 dsdt
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 embedded_controller/
-r-------- 1 root root 0 2006-07-04 20:31 event
-r-------- 1 root root 0 2006-07-04 22:15 fadt
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 fan/
-r--r--r-- 1 root root 0 2006-07-04 22:15 info
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 power_resource/
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 processor/
dr-xr-xr-x 3 root root 0 2006-07-04 22:15 thermal_zone/
dr-xr-xr-x 2 root root 0 2006-07-04 22:15 video/
mingdao@titus:~$ cat /proc/acpi/fan/FAN1/state
status: off
mingdao@titus:~$ cat /proc/acpi/thermal_zone/THZN/temperature
temperature: 42 C
mingdao@titus:~$ ls -lh /proc/acpi/thermal_zone/THZN/
total 0
-rw-r--r-- 1 root root 0 2006-07-04 22:17 cooling_mode
-rw-r--r-- 1 root root 0 2006-07-04 22:17 polling_frequency
-r--r--r-- 1 root root 0 2006-07-04 22:17 state
-r--r--r-- 1 root root 0 2006-07-04 22:17 temperature
-rw-r--r-- 1 root root 0 2006-07-04 22:17 trip_points
That box doesn't have everything that ACPI should contain, and it's the best I've got. And it doesn't work if I compile ACPI as modules -- they have to be built in, iirc. (I can't get into my BIOS on that box anymore, either.)
For my PCs, the only thing I've found to monitor these things that works is lm_sensors. I've got it working on a few boxen, but that depends upon the hardware.