@Mr. B,
You have to go back almost to the beginning of this story (Reply#10) (we are on Reply#33) to see what I said then:
Each door or window is a separate location. Unless you are prepared to run security alarm type plastic sheathed multi conductor wiring from every single door or window sensor to 'base' control station where they connect to the arduino (which has an xbee shield), I don't see this as being doable with the allotted budget.