You guys/ladies know the history of that song, right? Bukka White is credited with writing it (though, with the old blues stuff, lot's of songs seemed to be floating around that were first recorded by, and then identified with, one person). He was BB King's cousin, and if memory serves, gave BB his first guitar. He was also one of the early 'rediscovered' blues guys whose knowledge, once tapped by the "blues cult" of the early '60s, helped lead to finding other famous bluesmen from the Delta. Zep's "Hat's Off" is basically a clone of "Shake 'em on Down" and as far as I know, had little to do with Roy Harper, who is a magnificently quirky artist.