Ian is right. Depending on how old the car is, you can probably monitor those 2 parameters via a CAN bus. My car has 3 CAN buses, and from what I understand that's a pretty common arrangement. There's one CAN bus for the entertainment (GPS, radio, etc), one for the body(door locks, turn signals, etc), and one for the engine(ignition state, engine speed, etc). The specific state of the ignition switch is almost certainly on the engine CAN bus, but all 3 busses will have some flag telling them whether or not the car is running. As for the A/C, I'm thinking engine bus once again but it may be the body bus.
Interfacing the CAN bus is the most elegant solution, but it's not the easiest to implement. Depending on your experience level and resources, the easiest solution would be to go the route Ian suggested and simply splice into the switch for the ignition and the switch for the A/C. You'll need to use a couple of transistors or a logic level converter since your PIC can only withstand a maximum of 5.5V at its I/O pins. Maybe something like this
SparkFun Logic Level Converter - Bi-Directional. I know it says it converts between 3.3V and 5V, but it should work to step down 12V to 3.3V which is what you'll need.
As far as what you'll need to do for the PIC, do you have any programming experience? What languages? What compiler/IDE do you use? And, what do you want to have the PIC do once it detects that the engine is running and/or the A/C is on?