Eric Clapton did an album with BB King, who did an album with Eric Clapton who did an album with BB King who did an album with Eric Clapton who did an album with BB King
It's pretty awesome. I actually didn't like the gift shop and was turned off by the lack of attention to the "classic rock" bands (Zep, the Who, Queen, Pink Floyd, CCR, Skynyrd, Allmans) and how they completely ignore prog (Rush, King Crimson, Jethro Tull and so on).
Umm, this is kind of hard to put into words. The rhythm plays....rhythym parts. Usually thats just chords that fill in the sound and keep time.
Lead plays, I guess, the more challenging parts. They'll solo or play something outside of the basic riff.
If you're a Queen fan, listen to "Tie Your Mother Down". If I'm not mistaken, during the solo you can hear Brian playing the riff (rhythym) and soloing (lead) over it.