Right, I've no idea how I came up with this, but anyway...
*Goes and stands in the dead centre of the room, facing the puzzle wall*
*Shouts "Please let us in!" *
By reasoning thus: centre of the room for all the X marks the spot and lines business (more in hope than expectation), and then I'm thinking the rest may be an obtuse reference to that Moria puzzle in the Lord of the Rings, and we just have to work out what the magic word is.
Of course, it may mean we all get round the edges, and do something...
Passwords I decided not to use, for reasons of crapness and frivolity: "We brought a bottle and everything!", "We RSVP'd ages ago!!", "Open up, this is the police", etc