I guess it depends on the motherboard you are using, In my case (Intel D865 PERLK), I did not even have to edit the /etc/rc* files. All I needed was to install lm_sensors and it's libraries, run sensor-detect script answered yes to allow detection of IC2, but no to ISA , and finally edit the /etc/modules.conf to add:
#----cut here----
# I2C module options
alias char-major-89 i2c-dev
#----cut here----
Once I rebooted, sensor was running and I just had to configure gkrellm to get motherboard info (temps, fan speed, voltages).
Here is a good how to link on to set up lm_sensors from Linux Journal: sensor setup.
cyclo