Roberto,
I think that your solution should be fairly simple: It requires a hardware component that you may already have, (a USB to Serial adapter to go from the USB port to your serial device) and configuring the port on the PC in the typical way, i.e. Control Panel -> system (icon)-> hardare (tab) -> device manager (button). Then click on the desired COM port (i.e. COM1 or COM2 or ...)and setting its configuration to your desired settings (to match those of the device you are talking to). Once you have done these things, all of the standard library calls for rs232 should apply.
Hope this helps,
Ryykker