Canon Rebel T2i. Buy a refurb Directly from canon
http://shop.usa.canon.com/webapp/wcs/stores/servlet/product_10051_10051_267070_-1
They're out of stock now, but check back every so often.
Yes, it's a little above your budget, but not much. And for that money you get a serious "no excuses" package that will also hold its value should you decide to bail out. You also get an incredibly powerful tool for shooting HD video. It's really obscene how good of a camera it is for so little money.
I have a Canon 60D and a T2i, and the T2i has actually shot a couple of our covers recently.
Like any hobby, the real money is in the accessories. In the case of photography, that means lenses. Start out with the kit lens, and as your skills and interest grow, so will your collection.
As for learning, there's plenty of options. There's plenty of good websites that run you through the basics of what different settings do, and with digital photography, trial and error is an exceptional learning tool as additional shooting costs you nothing and gives instant feedback.
There's also the adult ed route. Most communities that have adult and community ed programs will offer a photo class, and many of them are quite good. I know the two folks who teach here in Flagler,and one's a news photographer and one's a portrait photographer, so students get a good look at different styles. There's also photo clubs in every town in the world, and going to a meeting, standing up and saying "I'm new here, help." will likely get you hooked up pretty well.
As for used, unless the deal is a screamer, I'd say stick with new or refurbs. The stuff holds its value pretty well, and the prices of new gear is pretty favorable right now. May as well spend the extra few bucks, get the warranty, and not have some dude's sweat all over it.
jg