Also, one more thing.
Try not to get too carried away with yourself. I think you might be having delusions of grandeur. This whole "infrared" lock thing would have been exploited a long time ago if it had been easily hackable. Even if it wasn't, it still would have happened. In fact, I bet that if you just take the time to google around, you'll probably pull some information on car alarm hackers that just scram through all the normal FM transmitters as fast as possible until you hear the car beep, and then it's time to go.
Some of the smarter car thieves have this. But then again, after you disable the alarm, you still have to either use a slidehammer to jack the ignition or just plain hotwire the car (providing it doesn't have either a Passlock (I or II) or a VATS system). So why not just make it easier on yourself and smash out the window, since you'll be tearing apart the dash anyways?
So why don't police and repo companies and locksmiths possess such a device? Maybe they do. But why? They could just as easily pick the lock. It's all really a matter of how "high tech" they want to get.
My advice: Don't bother. But if you really want to be Joe Cool and unlock your car with your PDA while hax0ring the White House and programming a robot to do your bidding, then just find out some information about pulse width modulation, figure out how to program the LED to flash on your PDA (might be a whole new project on it's own), and then write a program to scan through the possible pulses. I seriously doubt that they would have keyed the infrared to one pulse...... But it's possible, so who knows. Good luck.