Personally, I wouldn't use a resistor, it's just dangerous. Please consider using an opto-isolator, and take a look at this link;

http://www.8051projects.net/_zero_crossing_opto-triac

It's simple, inexpensive, and unlike the 1 meg resistor, it gives you some isolation so that a spike doesn't come through and fry you or PIC.

I built an IR remote system using Bruce's IR decoder chip, my Sony television remote control, and some X-10 modules. Sit on the couch, aim the remote away from the TV and toward the circuit, and turn on different lights. Then I added a modem so that I can turn the lights on and off using text messages. I used a 16F877 with Darrel's Instant Interrupts, so I'm sorry that I can't help you with the 12F chip and interrupts, but I'm sure someone else will chime in.

Good Luck,

Jerry