I recently played a PAL DVD on an Apple mini-mac. It played perfectly. It did not play on my regular NTSC DVD player.

The incompatability between PAL and NTSC lies primarily in that they have different resolutions and frame rates, which is a problem when using a normal TV or DVD player, as they often don't support converting these. This isn't a problem when using a computer because your monitor has a resolution and and frame rate much higher than either PAL or NTSC and so will convert either of them with no problem. So can you play PAL on any PC?: yes. However there is a major problem. Commercial DVDs and players are usually region coded and will only work together when the region matches. America uses region 1 and most PAL countries use region 2. A PC DVD drive will usually allow you to change which region it is set to, but only a few times. So if you only play PAL DVDs on your American PC, there is no problem, but if you want to play both PAL and NTSC DVDs you can't keep on switching between region 1 and 2. There is an easy way round this, though. PC DVD drives are very cheap, especially second hand ones. So you can get a second DVD drive and have one set to region 1 and the other set to region 2. Then you can play anything you want. Some drives are region free and can play any disc, and for some drives it is possible to flash the firmware with an unofficial version that changes them to be region free.