Sony DVD players, like most DVD players made by major electronics manufacturers are released with the ability only to play DVDs released in specific regions. This "feature" is implemented at the request of movie studios, who want to control when certain countries get certain movies. But if you want to enjoy the latest import on your domestic player you can usually disable the region encoding by using your remote control.
Get the model number of your DVD player. Different players have them in different places, but you can usually find it on the back. It will be a combination of numbers and letters, like DV487 or DHR-8105. If you still can't find it, check your manual. It should be on the cover or on the warranty page.
Write the model number down and go to Video Help's Region Code Hack message board (see Resources). This site is constantly updated with the latest region hack codes for players all over the world. In the search section, type in your player's model number exactly as it appears on the back of your DVD player or in the manual.
If your player comes up on the website, follow the instructions step-by-step. They usually involve opening the DVD tray and inputting a code on your remote control. If given the option to set the region code be sure to select "zero" as that will unlock your player for all regions.
If your player didn't come up, try DVDRegionHacks.com (see Resources) and follow the same steps as above.
If all else fails, do a search online for the player's model number and the words "region hack" in quotes. If there is a hack available it should show up. Not all players have hacks, so you might be out of luck. If you decide to buy another player do a search beforehand to make sure it has a region-free code. While changing your player's region code should cause no problems, it will most likely void the warranty. Perform at your own risk. If a disc is PAL and your system is NTSC (or vice versa) you still might not be able to play the disc on your player.