Re: Am I interfacing the keypad to the PIC controller correctly ?
You can delete the resistors by using internal pullups. They work fine for keyboards like this.
Floating inputs is not a good idea as all sorts of weird things can happen with the processor and leave you scratching your head trying to find the problem. (It worked yesterday, why not today)
Why not try one of the newer PICs, then you can use open collector outputs for the columns so they only pull low which is what you want and no external components at all other than the keyboard. Otherwise, as mentioned you will need to isolate the columns with diodes.