If you're running from CD, try the cheatcode noacpi.
If you have a hd-install do either:
apt-get --purge remove acpi acpid (to nuke it from your system)
or:
update-rc.d -f acpid remove (to stop it from starting)
Just removing acpi with update-rc.d will leave acpi on your system, so if you're in the habit of upgrading with apt, the next time acpi gets upgraded it's added back and you have to remove it again.