Every
DVD has a
region code recorded onto it.
DVD Players are supposed to
refuse to play recordings when the
region code does not match.
Currently, this matters if you live outside region 1 (North America), since the Americans get a lot more DVDs, earlier. What's more, when films get released elsewhere on DVD, they tend to be missing many of the extras (alternative soundtracks, trailers, deleted scenes etc) present on the region 1 version.
Americans may now be pining for the ability play material from other regions, since the BBC has begun to release Region 2 DVDs of such classics as The Black Adder and Monty Python's Flying Circus.
If this matters to you, try and get a multiregion DVD player. This may involve having someone hack your player, or you may be lucky enough to find a player which the manufacturer has slipped out with multiregional capabilities. Sometimes there are "secret" handset codes that change the region of the player.
Also, get a player (and possibly a TV) which is capable of handling both PAL (the European and Australian TV standard) and NTSC (the rest of the world's TV standard).