3pi Robot with Bluetooth
I would use bluetooth, it is easier to communicate with a computer. All you need for bluetooth is the module such as the BlueSMiRF from sparkfun and a Bluetooth usb dongle. Then all you would do is use the serial capabilities on the 3pi to communicate with the computer through the Bluetooth serial connection with a program like Hyperterminal. On the other hand, with the xbee you would need two transmitters and a way for the data to be read by a computer. One way to do this is through the Xbee Explorer. Both options would be the same cost but the Xbee route takes more components and is more complex. This page shows you how to establish the virtual serial port, and this page shows the connection, although it is for the Lillypad. You connect the VCC and Grounds of the 3pi and the Bluetooth then connect the RX and TX of the 3pi to the TX and RX of the Bluetooth module respectably. Hope this helps. Also Here is the tutorial for the 3pi serial communication.