You could also purchase a USB to serial lead.
Here the serial is connected as usual to the serial input and the USB connects at the PC/laptop via the USB port but it appears as a virtual RS232 port within the PC. Essentially the USB becomes transparent to the serial comms.
Some software does run into issues due to handshake or unusual configurations but most runs transparently. I have used these for getting oscilloscope data into the PC and stepper motor control successfully. Many have the FTDI chip mentioned by tpetar built into the USB plug.