Aftermarket Keyless entry

Has anyone installed one of those aftermarket keyless entry systems on a car that already has power locks, but not the factory option? I see some that also include remote starting. I was wondering if they are plug -n- play or do I have to run wires to the door switches...

-OR-

Is it possible to get a new/used factory module w/ fobs?

I have a 99 GA se if it matters. (I checked the codes and I do not have the factory option)

THANKS in advance,

Mark from Bucks Co. PA

Bump