I just tacked a full-sized flannel sheet to the wall of my computer room. I used map pins; they're not too hard to remove. I've also heard of folks using an oilcloth tablecloth, the kind with the fuzzy backing (fuzzy side out of course) and taping that to the back of a door.
My main advice (through experience) is that whatever you decide to use, be sure it's in a spot that you can step back from (hall way will not do; I tried it and there's not enough room to step back and "see" the whole design).