Apple (AAPL) is on the "Highway to Hell" now that it's finally signed rockers AC/DC to its iTunes music store. The top online music seller announced Monday that it had reached a deal with Columbia Records to make AC/DC's entire catalog available for download. That includes such hits as "Highway to Hell," "Dirty Deeds Done Dirt Cheap" and "You Shook Me All Night Long." The Australian rockers were one of the key holdouts left for Apple to sign after