It would probably best to use the WiFi do your long haul with an ad-hoc or mesh
network. You'd be surprised as to how much distance you can get with most
WiFi routers. Add those longer antennas and get much more. I've seen 7-miles
between two WRT54G with the LinkSys 15-dBi addon antennas.
Then use an ethernet shield and Arduino to connect your ZigBee network to your WiFi.