I wrote a tutorial on how to interface a Visual Basic program with Arduino. It includes downloads you can open in Visual Studio and the Arduino IDE. The executable is also available if you just want to play with the example program. The example program lets you send a pin number and delay value so that an LED on the selected pin will blink with a delay that is determined by the value you send it. It also receives a success/error flag from the Arduino.
Check out the two Arduino project videos I posted that uses serial communication with a Visual Basic program: