you can use g_serial without serial cable. Its using the USB (like a serial - usb coverter and then on the pc a USB to serial converter. BTW which firmware are you using? Mine works on cramfs from oddbot and als the one which comes wit Qtopia from NK.
OS8 worked on mine. did you rename to disk.hfv? and the rom to rom? It quits if it cant find rom but it should show the disk missing icon if you start without disk