Programming is hard but the Arduino is one of the easiest ways to get started. It's "different" from almost anything else not everybody can be good at it. People who are good at math, logic, and puzzles usually make good programmers.
Do you know any electronics? The Arduino is half-hardware and half-software.
I always say... The best way to learn anything is by taking a class. Books are 2nd best, and the Internet is the hardest way to learn. The Internet is a great reference, and there's enough information on the Net to learn brain surgery, but most doctors have gone to medical school. Most professional programmers and electronics engineers also have college degrees.
That said, I'm pretty sure most Arduino users probably taught themselves.
The problem with most books is that they teach a particular programming language without teaching the "big picture" concepts of what programming is all about. Once you've learned one programming language and the basic programming concepts, it's not too hard to pick-up a book or go online to learn another one.
Your project shouldn't be too hard. Can you run a wire from the PIR or does it need to be wireless? If you can use a wire, the hardest part is wiring-up the LCD and figuring-out how to use whatever library communicates with it. Wireless communication will again require a library that you'll have to figure-out, and probably Arduino on both ends.