DuracellEnergizer said:

SilverWook said:

I don't think Sith can appear as ghosts. Hologram or a Sith holocron image is another matter entirely.

Normally, I wouldn't bring this up, but seeing as you mentioned a Sith holocron, which is itself an invent of the EU and doesn't feature in any of the films ...

Lucas got the name of Coruscant from the EU, so I figure the door is open to such things. There's no reason Luke or someone else can't find one in a desolate ruin somewhere. It doesn't have to be overly explained to the audience what the gizmo does once it's seen in action. In some ways they are like the Kryptonian crystals in the Superman films.