Well, you could use your USB port as a serial port with a USB to serial driver or something, then write and read to that port, it's so easy.

Edit: Under Linux you should open /dev/ttyUSB0, under Mac OS X, /dev/cu.usbserial###### or something like that, I think the real problem is under Windows, where it's kinda complicated.

That's how the Arduino gCnBridge software & hardware works, but the Arduino has to do the translation to and from CALCnet 2.2 from/to serial.  You can't simply use the USB Silverlink or Direct USB link as a serial device.