Please help! Comparator function 12F635

[FromTheCockpit]

Hi, I have couple of 12F635 and I am trying to build an project with them where they send an RF signal when one particular pin is made high by an PIR sensor module.
I am planning to run this PIC on 3AA batteries 4.5V total. As an added feature I would like to make its any one pin high if the voltage falls below a certain predefined level (Anything between 2 to 4.5 volts-set in the code) and PIC to stay asleep untill either PIR puts its pin high or voltage falls below certain level.
I need guidence on two things:
1) Interrupt
2) Voltage check
I have read about both of the above topics but I am still confused with the voltage check mainly. I have never done anything like this before and would like some guidance on how to go about the code for this.
Any help will be appreciated.
Thanks