On paper, Walk Hard: The Dewey Cox Story — a Judd Apatow-produced spoof of musical biopics like Walk the Line and Ray — seems like another cheap-and-easy parody flick. But if the new, Internet-only R-rated trailer is any indication, it could be, at worst, a really funny cheap-and-easy parody flick. As singer Dewey Cox, John C. Reilly demonstrates impressive vocal chops, swaps spit (literally, ickily) with Jenna Fischer, and humps a groupie while bellowing, ''This is a dark f---ing period!'' Here's hoping the Man in Black is rolling in his grave, laughing. A