This is wrong, one the one hand acerhk is patched into our kernel for ages already, on the other hand acerhk and its custom ioctl interface only covers old notebook generations (built until 2004); newer ones use acer-wmi (or acerhdf for netbooks), which is mainline as well. acerhk-source is obsolete and not to be used on aptosid, otherwise stuff breaks.
apt-get install acerhk-source
m-a a-i acerhk-source
You have to rebuild the module after installation of a new kernel.