.RAR sounds like its an archive file which means you need to download WinRAR (equivilent to Winzip).
Now when you download this WinRAR at http://extratorrent.cc/search/?search=winrar&new=1
you should install WinRAR and then try opening your Video file as normal.
The file will recognise its a WinRAR file and automatically run the WinRAR application. Extract the files to maybe My Documents (XP) Documents (Vista) and then try the extracted files with your player.
The reason i state my documents or documents is some people extract files and don't know where they go - so make sure you tell WinRAR where to put them.
NOW here's the big finale If the WinRAR file asks you for a password - Allan you probably downloaded a fake file as password protected files are sometimes viruses or ask you to click an Url/Link to where you don't want to go.
So be vigilant.
In future - check the comments of any torrent downloaded as users may have stated this - but we cant remove it from our system unless you guys report it to us.