Reset dvd drive region
Unless you are willing to research how to flash the firmware of the particular DVD drive in your Mac to change the region, or to make it region-free, I suggest you try the very cool (and free) app VLC Media Player from VideoLAN. If VLC does what you need it to, please consider donating to the 'cause'.

Your milage may vary. 

Disclaimer: I have no financial stake in VideoLAN.org - I'm just a very satisfied customer.