You can use serial to send data to the Arduino - below is a simple bit of code to send individual letters via serial when you click buttons on a form:

Public Class Form1

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        SendSerialData("r")
    End Sub
    Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        SendSerialData("g")
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        SendSerialData("b")
    End Sub

    Sub SendSerialData(ByVal data As String)
        ' Send strings to a serial port. 
        Using com4 As IO.Ports.SerialPort =
                My.Computer.Ports.OpenSerialPort("COM4", 57600)
            com4.WriteLine(data)
        End Using
    End Sub

End Class

If you copy the code from above in to your form you will be able to see how it works - this code just changes the RGB led colour on a button click (you need to code the Arduino to read in this serial data and set the appropriate colour).

The Arduino code could look something like this:

const int redled = 9;
const int greenled = 10;
const int blueled = 11;

void clearleds()
{
     analogWrite(redled, 0);
     analogWrite(greenled, 0);
     analogWrite(blueled, 0);
}

void setup()
{
     Serial.begin(57600);
     pinMode(redled, OUTPUT);
     pinMode(greenled, OUTPUT);
     pinMode(blueled, OUTPUT);
}

void loop()
{
     byte colour;

     if (Serial.available())
     {
           colour = Serial.read();

           switch (colour)
           {
           case 'r':
                 clearleds();
                 analogWrite(redled, 200);
                 break;
           case 'g':
                 clearleds();
                 analogWrite(greenled, 200);
                 break;
           case 'b':
                 clearleds();
                 analogWrite(blueled, 200);
                 break;
           }
     }
}

You just need to use the Serial.begin function in the setup function and then the Serial.available() function in the loop function in order to get access to the serial data.

You could trim the code right down so it just turns an LED on and off with a button push on the form to get the hang of how it is working.

Cool.

I really appreciate the fast answers.

Thanks a lot.