If you want just write "Arduino" you can simple turn on/off each LED and add a delay.
int led7 = 9;
...
int led0=2;
void setup() {
pinMode(led7, OUTPUT); // initialize the digital pin as an output.
...
pinMode(led0, OUTPUT);
} //End of setup
void loop() {
// 01100001
digitalWrite(led7, LOW);
digitalWrite(led6, HIGH);
digitalWrite(led5, HIGH);
digitalWrite(led4, LOW);
...
digitalWrite(led0, HIGH);
delay(1000); // wait for a second
//and the others
} //End of loop
You can do this also by an Array or very flexible by ASCII-Code from a String.