you first need to download and run the prolific driver (either off the net or at fuelairspark,com , or from the xfi disc
plug in the usb and it should find the driver and install it (or do it manually and choose the prolific file from wherever you put it
go to you device manager and find the usb hub list
find the one that is the usb adapter (prolific)
open it and go advanced and find the com port that the pc assigned to it, it could be as high as 20 on some Pcs
you can change the com port to one that the pc isnt using (check your list of other usb ports)
set it to a port between 1 and 12
now on fast top tab goto communicate> setup> com port> and select the port that the usb adapter is assigned in the pc
now either use the F2 key or goto communicate> connect and you should be in
in the future when you start up the PC put the usb adapter into the same usb port on the pc otherwise it will try to reassign it a new com port #
also if you close the pc and it sleeps you may need to unplug and replug the usb adapter from the pc so the pc can reestablish the com port