Region Free DVD from www.M-99.com

1. Press Setup on the remote control.
2. Press Stop on the front panel of the player.
3. Press Previous on the front panel of the player.
4. Press Next on the front panel of the player.
5. You should now be in a secret menu where you can change the Region from 1 to 6, or Bypass for Region free.
6. You can also disable Macrovision from this menu.

Note: for the 351, the method simply unlocks the region/version menu, rather than opening a hidden one. No Macrovision method neither!

1. Press the Open button on your remote control to open the drive tray.
2. Press the Select button on your remote control.  If you have no Select button, try the Setup button instead.
3. Using your remote control, press the buttons 4, 9, 5, 4 and 0, in order, one at a time.
4. You will now be in a new menu where you can change the region to 1 for region 1, 2 for region 2, and so on.

Some models may not respond to the method.

All from Remote Control:
1. Press Setup.
2. Press Stop. 
3. Previous.
4. Next.
5. The setup menu shows one more option "Version" - select it.
6. Select "Region Code".
7. With Up and Down cursor select Region "0" for region free.
8. Exit Setup.

1. Press the Open button on your remote control to open the drive tray.
2. Press the Setup button on your remote control.
3. Move the selection to the Custom Settings option.
4. Using the remote control, key in the following: 3, 3, 3, 3.
5. You will now be in a secret menu where you can change the region number, or Free (or 0) for multi-region playback.
6. Press the Setup button on your remote control.

1. Press the Open button on the front of the player to open the drive tray
2. Press the Setup button on your remote control
3. Using your remote control, press the buttons 4, 9, 5, 4 and 0, in order, one at a time
NB: You may need to perform this step quicker if this doesn't work as expected
4. The onscreen display will display the word Version
5. Press the Play button on your remote control
6. Press the Right button on your remote control to highlight the currently selected region number
7. Using the Left and Right buttons on your remote control, you can alter the region to 1 for region 1, 2 for region 2, and so on, or 0 for multi-region playback
8. You can also enable VCD and HDCD playback from this menu
9. Press the Setup button on your remote control
10. Press the Open button on the front of the player to close the drive tray
11. Power off your player
12. Power on your player
To convert this player to Multi-Region if the above does not work
1. Press the Open button on the front of the player to open the drive tray
2. Press the Setup button on your remote control
3. Using your remote control, press the buttons 8, 8, 8 and 8, one at a time

4. The onscreen display will display the word Version
5. Press the Play button on your remote control
6. Press the Right button on your remote control to highlight the currently selected region number
7. Using the Up and Down buttons on your remote control, you can alter the region to 1 for region 1, 2 for region 2, and so on, or 0 for multi-region playback
8. You can also enable VCD, HDCD and possibly even WMA playback from this menu
9. Press the Setup button on your remote control
10. Press the Open button on the front of the player to close the drive tray
11. Power off your player
12. Power on your player

Note the following extra instructions:

cure is to do exactly as hack says but after entering setup menus go to the preferences page and then enter 4,9,5,4,0 etc, this brings up a region menu which you can set from 0 to 6 using up and down arrows.
then press setup to exit.