I also had problems with hdparm (SG_IO: bad/missing sense data)
and now it is running fine with hd-idle.
I downloaded it via CVS and compiled as mentioned on the website.
The tool is loaded automatically at system startup with help of the /etc/rc.local script. ( line "/usr/local/sbin/hd-idle -i 1200 -a sda1 &" above the exit command)