A good place to look to find out about downlding movies is in the Tips & Tricks section of the forum. Any movie that is less than 50 MB is probably going to be fake or porn. If you're looking for full movies then cd size is what you should be looking for; eg: over 500 MB in size. the best formats to aim for on OSX are avi, mpeg/mpg, avi-divx.

You may have difficulty using QT to play all files. Might I suggest you also use VLC which will play everything except the odd wmv file: http://www.videolan.org/vlc/ (choose the nearest mirror site.)