Hi,
The concept of resistive touchscreen interface is very simple. The four wires are normally
1) VCC
2) GND
3) VX
4) VY
Connect VCC and GND and connect VX (Volatge of X cordinate) to one ADC channel and VY (Voltage of Y cordinate) to another ADC channel. Read the values one after the another which will give you the X and Y cordinate of the touch.
Xbee can be simply connected to the serial port, normally at a baud rate of 9600 or 4800.
Please explain what are your doubts regarding Xbee interfacing?