communicate between a desktop XP and a arduino uno

Using a usb connection from my desktop XP compter to my arduino uno, can I communicate back and forth. For example, using a progaram in C# in my computer, I would like to tell my arunio when to turn on and off digital pin 5. nickynichols

Yes you can. I have not programmed the PC side, only sent info from keboard thru the USB. Arduino side is very straightforward to receive serial input and act on it. http://arduino.cc/en/Reference/Serial

basics are: check if data came in with if (Serial.available() >0){

then read it into a variable to act in incomingbyte = Serial.read();

then act on it if (incomingbyte == value_you_want){ //act on it } }