Hold off on buying the Holy Grail DVD. The version that's out isn't too good. The Python gang is re-releasing the film into some U.S. theaters this summer to support the new improved Grail DVD. It's being remastered from the original tapes to improve sound and picture quality and will include new interviews, lost footage and other extras that are not included on the current DVD.
Side note: Michael Palin and Terry Jones went to Scotland looking for the cave of Caerbannong used in filming the killer rabbit scene to record an intro for the upcoming new disc. To the amusement of themselves, their film crew and all the locals, they were unable to find the actual cave.