One of the Xbees is connected to the USB Xplorer that's connected to the computer. The second Xbee is connected to one Xbee Shield that's connected to one arduino duemilanove,being powered trough a external power supply (VIN/GND).
I want that the xbee that's connected to arduino/xbee shield could change your power level on an autonomous way to save power, decreasing the power level when signal is strong and increasing when signal is weak.