it depends on your DVD drive. if there is region-free firmware available, you would download and install that. use apple system profiler to get your drive's model and check
http://forum.rpc1.org/dl_all.php for the available firmware. once you have upgraded your drive, you use
region X to reset the firmware counter. this gives you essentially an unlimited number of resets.
if there is no firmware available, you can use
VLC instead of apple's DVD player to watch your movies or buy an external DVD drive and set it to whatever region you need it to be.
-r.