Hi Art! The answer is that it depends. Most of the world uses so-called PAL video encoding, while North America uses an encoding known as NTSC. It has to do with frame rates and the way colors are recorded, but to make a long story short, if a DVD was made in a country that uses PAL DVD players (such as the UK), you may have problems when you try to play it on your DVD player here in the states. However, some DVDs are coded for both regions. Before ordering, you should ask whether the DVDs are PAL-only, or whether they can play on NTSC-region machines as well.
We're going to London on business next week and will be staying in a friend's flat, and we're bringing some movies with us. To deal with any regional problems, I'm bringing along my computer to watch them on.
I'm sure others with more expertise can chime in!
Good luck!
B.