Making a program that sends data to USB port
First, this is maybe a pure "software" problem.

If you need send data to USB port, you need do something in two levels.

Driver level: If your device is a commercial one, and if the vendor support you one driver, you can use it. But if not, you may need make it by yourself, or use the generic one. In Windows, there are kernel level and user level, both can be developed under WDK. And you can also use the generic one: http://www.libusb.org/, it can be used both on Windows and Linux, and easy to use.

Application level: You can develop your applications using your favorite language/IDE to communicate with your USB device through your USB driver.