When you rip a DVD before burning it ussually removes the region code. However you can try DVDShrink which allows you to select the region code(s) before ripping the files. Most (but not all) DVD stand alone players now have a button on the remote that enables you to switch directly from PAL to NTSC playback so you don't need to change the format of the disc.
Most DVD Players do not allow you to play differing regions without codes or some sort of tinkering inside the unit. You can get a program from Afterdawn that allows you to remove region codes. Go to the software section and type in region.