Set timer mode to mode 2 (8-bit autoreload). Calculate the reload value to put into timer holding register, enable interrupts and start timer.

There is an example (only the principles):

void timer1_interrupt () using 1
{
// your small portition of interrupt code here
}

main ()
{
TMOD = 0x02; // T0 - mode 2
TH0 = -84; // set reload value for 22 kHz
ET0 = 1; // enable timer 0 interr.
EA = 1; // enable all interrupts
TR0 = 1; // start timer 0

// your main program code

}