Hey just found out how to change the Arduino com port on XP:
Plug in the USB Arduino Board.
Open "Control Panel"->"System"
Select the "hardware" tab.
Click "hardware manager".
Select the Arduino Serial Driver properties as in this image:
http://tof.danslchamp.org/AXIC/ftdidriversettings1.jpg
Select the advanced properties:
http://tof.danslchamp.org/AXIC/ftdidriversettings2.jpg
Change the port number:
http://tof.danslchamp.org/AXIC/ftdidriversettings3.jpg
CLOSE THE "USB SERIAL PORT" PROPERTIES DIALOG.
UNPLUG THE ARDUINO BOARD.
Plug in the Arduino Board.
Magic.
/me