Well, can't say too much about what the cover should look like, aside from what's already been said. However, I do know what the promo poster (like packed with WiZARD! or sent to comic/bookstores to advertise new stuff, like “Kingdom Come”) should look like:
All-black background, faded close-up of the Ghost in the No-Ghost logo, with the words “They're Back.” Underneath that, in smaller text, “Open for Business Spring 2004, from 88 mph Studios.” And in larger text underneath that: “We're Ready to Believe You.”
'Course, that's just my opinion. Seeing something like that in my local comic shop or Waldenbooks would pique my interest, then give me chills, and I'd start to hyperventilate.
–Cliff