A quick no frills guide to updating your MacBook's DVD player for region-free use. The Google search term used to locate the rpc1.org forum thread is "Matshita and Apple RPC1 firmware: a summary".

WARNING: Be aware that these changes ARE NOT covered under warranty, so use the software at your own risk. Also, if your DVD player is not listed on the firmware page, then unfortunately you're out of luck.
Leopard (10.5.xx) users: The firmware upgrade will not work under Leopard directly, but a workaround has been found by Viddler user wimmulder so feel free to consult his advice & instructions in the comment he left (I have not personally tried wimmulder's method; I got lucky and used the hack while I still had Tiger installed).
*If any of this seems too risky, save yourself the time and money and just go out and buy a region free DVD player - they're cheap. :)