IF the password is complex characters (letters, numbers, symbols) and over 8 char. Don't even bother it will take days at a minimum and if it's any longer it could take months or more. I've yet to hear of any exploits for cracking the encryption. If you have an absurdly fast computer than you might have a chance otherwise it most likely will not be worth the time. Now, I assume your trying to open up a file with a cracked program or something as this I feel is the most common use of RAR password cracking so if it is just goto another site and look for the crack. If this isn't the case then you just may be out of luck.