Here is the answer. Most porn/movies/ whatever kind of video files/etc are still distributed through the internet via usenet/newsgroups/nntp( im sure many of you new kiddies dont know about). Before you guys get your movies/porn/etc through limewire, it always comes through usenet first. In order to post movies/binaries/etc on usenet, you must break your movie into pieces and send them as seperate files. the program/standard usually used to seperate them is called rar and is usually always disassembled/reassembled on windows. Then people download all the pieces and reassemble the rar files to make a whole movie file again. The problem is when the rar program reassembles the pieces again, it doesnt put it back to its 100% original form . Some of the header content from the rar program gets left behind inside of the movie file. For some reason, this causes the mac's implementation of the mpg reader to get messed up. I'm not sure who to blame, it could be mac for not implementing mpg good, it could be rar for not being "clean" enough during reassembly, or it could be windows for allowing a messed up implementation work in their media player. this problem SHOULD go away as people start to use more programs like limeiwre which dont require files to be disassembled and reassembled.
btw, new video/programs/content ALWAYS comes out on usenet first. if you guys camnt happen to find what you are looking for on limewire, you can try usenet, but be wrened, it is a 100 times harder to use than limewire. Usenet comes from the very veyr beginning of the internet. HAPPY SEARCHING!!!!