From my understanding, you can play any DVD worldwide-- whether in PAL or NTSC format, and any region code-- on a computer. I use a Mac, but I believe this applies to PCs as well.
I bought Ong Bak both in the NTSC and the PAL version. But is able to play only the NTSC on my player and the PAL on my computer.
If you enjoy watching international movies from all over, you may want to invest in a code-free DVD player. One good one for USD $150 is here:
http://www.codefreedvd.com/You can also convert your DVD player to an all-region player by purchasing certain hardwares, installing, and then reprogramming the player. I wouldn't recommend this unless you're good at this sort of things.
Another tip is to find the cheapest DVD players (around $30-40). They're usually code-free. Of course, make sure you research this out before you purchase it.
If you have purchased an original DVD that is a region other than the one your DVD player can play... and you're somewhat tech saavy, you can easily decode and convert the DVD to an all region DVD (region 0) using converting softwares, which you can then play on your player. This is also a great way to backup your originals or if you want to lend a copy to a friend and don't want it damage when you get it back).
For me, I can easily get any movie worldwide by simply researching it using Google then purchasing it online. You can also find most movies on Ebay, but beware, many of them aren't originals, and again, make sure you have the means to play it.
Hope this helps and enjoy.