Programing with USB

I I don't know if you can help me but I live in La Paz ,Mexico and can't find any help here.I have a PanSat 2700a and need to program it. I have the files on my computer and it takes a null modem cable. I've looked all over town for one with no luck and the mail from the states is undependable so I finely drove 100 miles to Cabo San Lucas and finely found a cable that had a 9 pin connector on one end and a USB on the other. I need to know how I can direct the file to the USB port if that is possible.I,ve been trying to solve this problem for quite a while and with my limited Knowledge of computers I don't know what to do,if you could help me it would be greatly appreciated. Thank You Tom Prease T wetired@nerdshack.com