Yeah I had a rar file like that once... I believe it was Freddy Pharkas... That was a while ago.
I tried using a brute force thing on it. I didn't get it tho. Basically the faster your computer, the faster it will take to crack it depending on how many characters.
Also when you open up the RAR file in WinRAR, check the properties or something. It might have it written in there for you. I have a file like that. I don't know why they bothered with a password when they just gave it to you