Input Capture issue with Mega

On Duemilanove (atemega328p), I can use ICP1 (Timer/Counter1 Input Capture Trigger).
It works well.

On the Mega (atemega1280), the ICP1 is not connected.
ICP4 and 5 are be connected, but I could not use them.
ICP3 does not seems to be connected.

void setup_timer1(){
  //disable all interupts
  TIMSK4 &= ~( _BV(TOIE4) | _BV(ICIE4) | _BV(OCIE4A) | _BV(OCIE4B) | _BV(OCIE4C));
 
  //set timer mode
  TCCR4A &= ~( _BV(WGM41) | _BV(WGM40) );
  TCCR4B &= ~( _BV(WGM42) | _BV(WGM43) | _BV(ICNC4));
  TCCR4C &= ~( _BV(FOC4A) | _BV(FOC4B) | _BV(FOC4C)) ;
 
  //capture raising edge 
  TCCR4B |= _BV(ICES4);
 
  //prescaler 1/8
  TCCR4B |= _BV(CS41);
  TCCR4B &= ~( _BV(CS42) | _BV(CS40) );
 
  //disable outputs
  TCCR4A &= ~( _BV(COM4A0) | _BV(COM4A1) | _BV(COM4B0) | _BV(COM4B1)| _BV(COM4C0) | _BV(COM4C1));
 
  //enable capture interupt
  TIMSK4 |= (1<<ICIE4) + 1;
}
 
ISR(TIMER4_CAPT_vect){
  unsigned char sreg;
  /* Save global interrupt flag */
  sreg = SREG;
  mesureTemps.courant.a=ICR4;
  SREG = sreg;
}

ISR(TIMER4_OVF_vect  ){
  noInterrupts();
  mesureTemps.courant.b+=1;
   interrupts();
}

thank you!

The thread below may help you, showing what is and isn't available, and also the pin mapping between the chip and arduino pins:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1245229578

thanks, I wil check that.