Can ardunio communicate with COM

I have a firmware device that has a serial port and a usb device, I can interface into this using visual basic.net and connect to the serial port and usb port (although the USB port on the device is not powered), can I use the Ardunio to connect to this device and change values via COM the same way I can with my computer and visual basic?

Thanks

You can do com port. If the input to your device is RS232, then you need a converter such as this unit Pololu 23201a Serial Adapter Partial Kit to convert RS232 to MCU voltage level. But you can not connect to USB port, because USB on your device is a slave and needs a master (computer or USB host device);

just connect db9 connector (if you device has one) to the converter I linked, and the TTL level RX and TX to the arduino. I'm sure you can find many sample codes for communicating over serial port with arduino.

I doubt there would be any useful shield for you. USB host is complicated; there are some USB host on the go (OTG) devices, that can host only specific standard devices, such as flash drives or mass storage devices. But for something to work with your custom device, it needs to be able to handle driver needed to work with your USB device, which makes it very complecated.

I posted some work here: http://www.circuitsathome.com/mcu/towards-an-ft232-driver-for-the-usb-host-shield-part-0

about connecting to FTDI serial ports using USB Host Shield. Do you know what USB device you have ?

Serial is easiest, but USB host does work.