How to create a 38 Khz pulse with arduino using timer or PWM?

I am experimenting with an infra red remote, sending my normal data that I usually send by radio modules, using VirtualWire, or maybe EasyTransfer later.

I am driving the base of an LED driver transistor , ( via a resistor ) with 38 Khz from a similar timer generator as Nicks ( but with one of 2 outputs for some reason dirt cheap wireless | CHEAP, FAT and OPEN ? )

The data I take from another pin ( using NewSoftSerial) to the base of the transistor with a diode chopping the 38 Khz stream.

It is working fine, and I want to try Nicks idea of reducing the duty cycle to pump the IREDs harder.
I am only sending a few bytes at a time at 2400 baud, and can afford to have 100mS gap between bursts to keep the average drive down a bit too.

I see the background 38Khz is all done in setup.

What are the implications with this if I want my remote to go into sleep mode ? ( The remote is 4.5 v battery operated )

This is my general enter sleep routine that I blatantly copied from Crossroads, with little knowledge of how it works :-

void enterSleep()


{
     
  /* Setup pin2 as an interrupt and attach handler. */
  attachInterrupt(0, pin2Interrupt, LOW);
  delay(50); // need this?
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);  // setting up for sleep ...
  sleep_enable();                       // setting up for sleep ...
  ADCSRA &= ~(1 << ADEN);
  PRR = 0xFF;
  sleep_mode();                         // now goes to Sleep and waits for the interrupt

  //************************************************************************************
  /* The program will continue from here after the interrupt. */
  detachInterrupt(0);                 //disable interrupts while we get ready to read the keypad 
  PRR = 0x00;
  /* First thing to do is disable sleep. */
  sleep_disable(); 
  
}  // end of  enterSleep()  function