You don't open it friend.
Download the file, extract the rar/zip using WinRAR. (Download WinRAR if you don't have it already). Once you have it you can extract all the files from in it. Now, you just install the hacked client (the .jar file you'll find in the rar/zip) by going to %APPDATA% and finding your ".minecraft" folder. Once in your .minecraft folder go into /bin/ and paste the .jar file in. Make sure it is named "minecraft.jar" without quotes.