TomTom 5 & Toshiba e800

I was given TomTom Navigator 5 software as a present and this installed with no problems on my toshiba e800. I then purchased a standalone TomTom wired serial GPS receiver. When I connect this to my PDA I am asked for the name of the driver for the unknown USB device however the receiver did not come with a driver. I have tried selecting the 'TomTom receiver' and 'other receiver' options under preferences in Navigator 5 but I cannot get the software to recognize that there is a GPS receiver attached. I have also tried completely reinstalling TomTom Navigator with the receiver plugged in and powered on but still I get the 'no GPS receiver!' message. What am I doing wrong?