You've got various options.
You can get a stand-alone DVD-player that you can connect to your Mac, and that does not have region limitations (such creatures exist -- Pioneer even has one you can install in your computer replacing the one that's there).
Or:
Which Superdrive do you have, the Matsushita or the Hitachi-LG? Check through About this Mac>More Info>ATA
The Matshita one now has double region check which is what is locking out VLC, etc.
BUT - go to System Preferences>DVD/CD and deactivate the behaviour to open DVD-Player when you insert a DVD. Just choose Ignore.
Some Intel Macs will play DVDs from other regions with VLC when you do that.
You can also try ripping a DVD to your hard disk using Mac the Ripper, and setting it for Region Free -- takes time, and not as convenient as popping a DVD in the player.
If you have no luck, you can try hacking the Firmware of your Superdrive. That's risky - I've done it on all my previous Macs though, without any problems:
Read the instructions religiously, follow them just as religiously. Find which drive you have as shown above - find the corresponding drive and Mac type in the list, and download what you need. Read all the instructions carefully and make certain you've understood them and are doing things in the right sequence, should you choose to go ahead with a hack.
Be aware that your WARRANTY is invalidated if you perform an unauthorized firmware change to your computer!
http://www.powerbook-fr.com/dossiers/dvd_region_free_en_article30.html