How can i change a video clip format that will play on a PC to play on my MAC

http://www.flip4mac.com/ supports all but DRM formatted Windows video. http://www.videolan.org/ and MPEG4Streamclip may support additional. DRM Windows video may require running Windows natively on your Mac. Or requesting the source give you an MPEG4 compatible format or Realplayer formatted file. Running Windows is described here: https://discussions.apple.com/docs/DOC-2741