just because it passes the POST test doesn't necessarily mean that the IDE controler has correctly detected it. Just try running the "detect IDE" function in the BIOS... it might work, but them I would have thought that the drives are detected in the start up anyway.
Just another idea... try the drive (ON ITS OWN) using cable select mode... It might help.
If it works then, at least you will know if it is the drive that is not working.
If it doesn't work in yours, try using the cable select mode in the other comp.