AVR ATMEGA88 PCINT PROBLEM

Hi,

I am trying to use the PCINT0 interrupt on the Atmega88 chip but an
unable to get it working.
i want it to work for pin number 12, 13 and 14 ie PCINT0, PCINT1 and
PCINT2 respectively.

i am initializing it as

main(){
PCIFR = 0X01;
PCMSK0 = 0X07;
Sei();
}

AND

ISR(PCINT0_vect){
send_byte(1);
}

The ISR is not getting fired using only this code. Am i missing out on
some initialization. Kindly help me out.

Thanks,
Rohan.

.