Peter O'Toole = Conan Doyle (Gullible)
Harvey Keitel = Harry Houdini (Amazing Randi-esque Mythbuster)
Paul McGann = No clue who he's playing in this, but hey.. it's Doctor Who. Who's complaining?
There's also the tall balding fellow who was in a few incarnations of Blackadder and was the mourning husband in the video for Kate Bush's "This Woman's Work".
PS: Have you noticed the ad for Oceanic Airlines with the three stewardesses? Try it. Just, just try it.
PPS: Alas, it's apparently some Lost fake-ad thing.
PPPS: The aforementioned film? Might seem to drag a bit, but the heart of the story is when Houdini's doing his water torture trick on stage and the parts that follow.