Originally Posted by Imkantus

K. Is there another device beeing connected to the same cable?
40-Pin IDE cable can connect a master and a slave device at a time - which one of them is beeing used as which is configured using a jumper you'll find on the back of any IDE device:

(1 = Master, 2=Slave)

Be sure to have the IDE device beeing connected to the outer-port, beeing jumped as Master & the one beeing connected to the inner-port beeing jumped as Slave.

I am running nForce 4 mainboard myself and expired my IDE configuration not to work properly on OS X without having it beeing seted up this way, although it worked fine on other OS with my previous configuration...
I hope this will gonna work in your case too.