How can you make a usb device for the PC with drivers and all so you can make the device conected receive a packet data from the PC and when that packet arrive to the device the device turn on a motor?

Answer

There are many USB chips on the market but it is too complicated for some home constructors, I will recommend the PIC18f2450 microchip, it can handle a lot of data and can drive a relay directly, so no need for a buffer, a data sheet can be downloaded from http://www.patenttrade.net and everything you need for programming it is available at http://www.pyrro.patenttrade.net .

Answer

Another option is to use a USB-to-serial converter. This can either be an IC included on the device, or as a separate device to control the motor-control device. Then, you can use any microcontroller to receive commands from the PC. The USB driver will create a serial port, which can be accessed by a terminal program (such as HyperTerminal included with Windows) or by special applications software that opens and communicates through the USB serial port.