So I posted a while back asking about vehicle locks, specifically on my 1995 Dodge. The (original) key that came with it would open the driver side door and operate the ignition, but didn't open the passenger door. My post was a dual-part question: I asked about replacing the passenger-side door lock, and I asked about some more info on how vehicle locks actually work. My intent was to replace the recalcitrant lock, then use the old lock for picking practice. The responses I got basically said to leave it alone and start with something easier (along with a few posts that outright accused me of using the forums for tech support, which was not my intent.)
At any rate, I went to a lock smith and had duplicates made of the key I had. It looks like the key was simply worn, as the duplicate opens the passenger door just fine, even though the original does not. My guess is that since the driver door and ignition lock see constant use (this vehicle has 265K miles on it), they've kind of gotten worn in tandem. The passenger door lock, being used rarely if at all, is probably still much closer to factory spec. So that basically solved the functionality part of my problem.
I'm still hoping to learn more about vehicle locks eventually. My pick set came with an odd-looking pick that was supposed to be for vehicular locks, and I can't quite picture how that would work inside the lock.
Meanwhile, I've picked up a mix of pad locks, mortise locks and plain old house locks from various sources (eBay, Home Depot, Ace hardware) and am spending a bit of practice time most evenings. Finally managed to pick a run-of-the-mill Schlage open yesterday; those turned out to be harder than I would have thought. But I thought I'd post this as just a conclusion to my Dodge lock adventure and what I learned from it.