Kremit is right. Scanners aren't ridiculous...about $60-$100 for low-end models. They're handy to have around, but be warned ALL your friends that have OBD-II vehicles will be asking to use it when they get a CEL

I don't know much about the software packages available, but some of them are pretty nifty. When Stolon visited he had some software on a laptop and we could monitor just about EVERYTHING while driving the car. We made him a CAI and did pre- and post-CAI intake air temps and found that it really did work.