You’re probably out of luck. Apple are dreadful for this, it’s one respect in which they’re much worse than Microsoft et al, because they have almost total control over the hardware they use.
In theory, you need to 1) apply a region-free firmware to your DVD drive, and 2) use Region X to remove the OS X region restrictions.
In practice, there aren’t any region-free firmwares available for the DVD drives used in the Macs I have owned, and you will probably find the same thing with yours. You can start with a Google for the relevant drive model and make (shown in System Information) and see if there’s anything available.
The only time I managed to read DVDs out of region on a Mac was using a region-free USB DVD drive in combination with Region X, but that was on Leopard not Snow Leopard. Even then I ended up having to use VLC to actually watch things, DVD Player wouldn’t work. I have no idea if it will work on 10.6. Probably not.
Good luck though! Please post if you figure out a better way of making it work…