Srikanth,
on my '592 I would try to use T2 for this job.

uC-Clock = 12 MHz (or 1 MHz external clock)
Prescaler = 1
Compare Register CM0 = 1..65535
External T2 Counter reset at every clock pulse on pin RT2
Clock output on P4

This should give you a programmable divider (register CM0) and an output clock from 15 Hz..1 MHz

I don't know if your uC got such a timer. But if not it's not a problem to use an external uC controlled divider. There's no need for a PLL if you use the controller clock as the source. Don't know if your ADC requires a synchronous clock at all.