Well, after some quick look up and I might have the answer folks !!!
If you use an UNO, Ethernet shield uses PIN 11, 12 and 13
If you use a Mega, Ethernet shield uses PIN 50, 51 and 52
Now stack the Wireless SD shield on top
Arduino TX(1) and RX(0) will be used for xbee
SDcard on Ethernet & Wireless SD can not be used.
Rest of the pins are all available. Hope we are correct.
Team BTF