Region settings on drives are a pain and usually have both a hardware and a software element; the first being Region Playback Control (RPC) and on almost all Apples is RPC-2.
as jimoblak points out, there are some utilities to update the firmware (hence overcoming the hardware element), but IIRC, you need to have a mac that can boot into OS 9 to run the updater. I think xlr8yourmac.com have a link on their f.a.q. to the relevant sites
You can then use a utility like RegionX to deal with the software element.
soi la, soi carré