Hi,
89C51 does not have internal RTC. Using 89C51 digital clock can be implemented using delays with respect to the oscillator frequency but it is not accurate. For accurate time calculation external RTC is needed. You can choose DS1307 RTC IC, easily available in the market.
Kindly provide the details of connections(LCD Port e.t.c) & also tell, do you have drivers written for 128 X 64 LCD.