back to the pings))

right so i have changed the code so that it uses the pulseIn function, it uploads to the board and works for a few seconds but doesn't sustain itself, i hope i haven't broken my adruino!
here's the code:

int pingpina = 7; // Ultrasound signal pin
int pingpinb = 8; // Ultrasound signal pin
long vala;
long valb;
int ledPin = 13; // LED connected to digital pin 13
boolean pulseAin, pulseBin;

void setup() {
 beginSerial(9600);                  // Sets the baud rate to 9600
 pinMode(ledPin, OUTPUT);            // Sets the digital pin as output
}

void loop() {
 pinMode(pingpina, OUTPUT);
 pinMode(pingpinb, OUTPUT); // Switch signalpin to output

 /* Send low-high-low pulse to activate the trigger pulse of the sensor
  * -------------------------------------------------------------------
  */

  digitalWrite(pingpina, LOW); // Send low pulse
  digitalWrite(pingpinb, LOW); // Send low pulse

 delayMicroseconds(2); // Wait for 2 microseconds
 digitalWrite(pingpina, HIGH); // Send high pulse
 digitalWrite(pingpinb, HIGH); // Send high pulse
 delayMicroseconds(5);
 digitalWrite(pingpina, LOW); // Send low pulse
 digitalWrite(pingpinb, LOW);
//

 pulseAin = false;
 pulseBin = false;

 pinMode(pingpina, INPUT); // Switch signalpin A to input
 pinMode(pingpinb, INPUT); // Switch signalpin B to input

 while(pulseAin == false || pulseBin == false) { // Loop until both pins reads a high value
 if( digitalRead(pingpina) != 0 && pulseAin == false){
 vala = pulseIn(pingpina, HIGH);
 pulseAin = true;
    }
if( digitalRead(pingpinb) != 0 && pulseBin == false){
 valb = pulseIn(pingpinb, HIGH);
 pulseBin = true;
    }
 }
 /* Writing out values to the serial port
  * -------------------------------------------------------------------
  */
// do the scalling of your results here
  Serial.print("Sensor A value =");
  Serial.println(vala);
 Serial.print("Sensor b value =");
  Serial.println(valb);
delay(40);
}

it seems like it works but it just doesn't last very long and sort of crashes! does any know what's going wrong? Any help will be greatly appreciated.
cheers