You can extract files from RAR archives downloaded from Rapidshare with SuperNZB’s free RAR decoder:
(Note to Mac users: Download with Safari if your browser doesn’t know what a DMG file is.)
Many RAR files originate on Usenet and are then uploaded to Rapidshare. However, Usenet does not have built-in error-correction, so it is common to find RAR files with minor corruption. And that will prevent you from extracting the contained files. The good news is that RAR files are almost always posted along with PAR error-correction files. So, if you have a damaged RAR archive, look for the associated PAR files. Once you have them, you can use SuperNZB’s PAR decoder to fix the RARs, and then extract the files.
Learn more about RAR at RAR Files Explained in Plain English.