Just to dig into technical stuff, in case someone is interested - apologies for the tedious subject.
There are several different standards for videos. The main are NTSC and PAL. They have some slight difference in the size of the frame, and the frame rate (let's call it "speed" to simplify).
USA uses NTSC, Europe uses PAL. France had another format (SECAM) for VHS tapes but they are using PAL since the DVD format was introduced.
Now there are Regions. Regions are not format. They are codes written to the DVD to let it play on specific dvd-players.
DVDs have the ability to encode an option which specifies which regions in the world the discs can be played. The movie studios have collectively divided the planet earth into zones which corresponds to their distribution system.
The main reason for it is that a while ago the delay in the theatrical release dates between the US and Europe was quite big - and you had movies released on DVD in the States while they did not reach cinemas in Europe yet (this still happens sometimes, but more and more movies have a simultaneous worldwide release lately).
Also, some DVDs are regionally encoded for rights issues (companies have rights to publish some material in a specific country - without code and with internet shopping that would be a "worldwide release" instead).
Without regional code, US imported DVDs were appealing for European customers who wanted to get the movie straight to DVD and "skip" the theatrical release at once.
Regional codes do not allow you to do this - as you can basically play a US dvd on a player manufactured for the US market. DVD-rom players on pc have the same thing (but they let you switch between regions a certain nuber of times, then they stick to the last region you used).
Now, you can find region-free players, and you can also make a player region free with a small firmware upgrade (easy to do it yourself or at a pc/multimedia center - keep in mind you usually invalid your manufacturer's warrantly doing so).
Besides, the most part of DVD player play both NTSC and PAL discs. And so do the DVD-roms on pcs/mac.
The problem is all in the regional code - for example there are music videos released in the US that are NTSC and Region 0 - meaning that any player from any country will be able to read them.
Finally, there are a few weird cross cases. Japan has the same regional code of Europe (Region 2) but the same standard of the US (NTSC).
Region Countries
0 No Region Coding
1 United States of America, Canada
2 Europe, including France, Greece, Turkey, Egypt, Arabia, Japan, South Africa
3 Korea, Thailand, Vietnam, Borneo and Indonesia
4 Australia and New Zealand, Mexico, the Caribbean, and South America
5 India, Africa, Russia and former USSR countries
6 Peoples Republic of China
7 Unused
8 Airlines/Cruise Ships
9 Expansion (often used as region free)