Resetting XBee with an Arduino
The reset pin is bidirectional, and default configured as open-drain with a pull-up resistor (datasheet page 13). That means that you can assert Reset by making that pin low.   

Don't make the Arduino's output high to de-assert Reset! Two reasons: 


Xbee are 3.3 V devices, and 5 V on the input may damage them  
If you would make the output high (whether 3.3 V or 5 V) and the Xbee would make it low you would have a short-circuit.  


So to de-assert Reset switch the Arduino I/O pin to input. Make sure the ATmega's internal pull-up is disabled! The Xbee's pull-up resistor will take care of the proper high level. 

To interface the 3.3 V Xbee safely with the 5 V Arduino you can use LadyAda's adapter which has a level shifter.