A .rar is a compressed folder, like a zipped folder. You need to unzip it with something like 7zip:

7-Zip - Free software downloads and software reviews - CNET Download.com

Once you've unzipped it, you can see what format the files are in. They are most likely mp3 already, but inside the zipped folder. Once you have run 7zip, you should have a new folder with the tracks as mp3 inside.