Hi Raghu

I guess that you want a compact ( small) keyboard and a PC keyboard is to big. Also that you want to drive the keyboard with the less amount of lines.
I often face this problem and for some cases I put a shift key associated with a led ( if possible put the led inside the key). Every key has written two symbols ex. A/B ( remember the telephone keyboard). If you want to input the A just press it. When you want to input the B you first press the shift key ( the led will lit) then you press the A/B key to input the B.
And after this the led will go off and you go to the original stage automatically ( without the the shift).
Also if you have a buzzer to make a auditive feedback you can use two differents tones ( with or without shift key activated).
You will be surprise how friendly is this for the final user.
Also the bit use for driving the led can be use for knowing from which look up table you have to decode the press key.

This approach is useful for having a small and less expensive keyboard ( not really for minimazing the quantity of keyboard driving lines)

Good Luck
Daniel