Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
.RAR files are compressed archives.

Use the Unarchiver to open it and extract any contents (i.e. the video file you are after).
 
Some people are just retarded. .rar is archive but you can play them like a video file too. Right click on it and select open with and open it with VLC. If you don't have VLC, google it and download it.
 
how to "play" .rar files

Drop the file on Stuffit Expander and the vid will appear. (If the file is in parts 1, 2, 3, 4 etc have them all downloaded together so Stuffit can merge them.)
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.