Best way to crack .rar archives?

Snowraver1 writes: Occationally after downloading files from the Internet I'll notice that the file downloaded is a .rar file within a .rar file. The first "layer" of raring is not password protected, but the .rar file that gets extracted from the first archive is password protected. What I'm left with is a password protected .rar file and anger. My question to everyone here is: What is the best way to crack a password protected .rar file? I have seen some crappy shareware brute force type programs, but I was thinking something more like RainbowCrack. Is there a way to extract the password hash value from the .rar archive and use RainbowCrack to crack it?