Hi Paradigm;
If your proc has PORT Change Interrupt (at least on 4 pins like almost all PICs on PORTB) and it can wake-up from SLEEP (see your datasheet) then it is possible using only one interrupt (this).
For example set all 4 keypad columns to zero and pull up (as usual) the rows to VCC. If the 4 rows are connected to the 4 input pins capable PORT Change Interrupt, interrupt occurs (the proc returns from SLEEP) when any key pressed, because the PORT (any of the 4 pins/bits) is changed.
Then, as barry wrote, you will still need to do a scan (even in the interrupt routine) to determine which switch was pressed.
A word of advice: use a short delay (15..20 msec, for debouncing) before scan the switches.
zuisti