My 4 cents...
Poker books: Brunson's Supersystem II is almost like a foundation. I also recommend Sklansky's "Theory of Poker". If you want to play in tournaments, I highly recommend Harrington on Hold 'em Vol I and II. I also advise that if you read these books, to read them one at a time, let it sink in, and play a little before moving on to the next book. Otherwise, it is just too much to absorb and you'll find yourself more confused than anything.
Online poker: Yes, it is true, you have to download each site's software to play, but the advantages of online poker are too numerous to mention here, the most obvious being there is always a game and always people to play with. If you play online, I do not recommend playing the play money games other than to familiarize yourself with that specific site's betting buttons. Every site has a slightly different user interface, so it is worth it to familiarize yourself with it before playing for real money. The problem with the play money games is that no one takes it seriously and will play any two cards. You won't learn anything playing this way.
Playing in the casino: Playing in a casino against live competition can be an intimidating experience. I'd suggest playing in a few "friendly" home games, and then going with a home game buddy to play at the casino. Having a buddy there helps, believe me. If you play online at all, you'll see that online and live poker are very different animals. I don't think the skill level of the competition is all that different, but players tend to be more aggressive online for some reason.
Playing live, there is more information to process. There is how your opponent handles his chips, how much he bets, how long it takes him to bet. In general, I don't think recreational players should get too worked up with trying to read "tells", or getting too much into macho stare downs with opponents. That stuff only works on TV. If you stick to the basics, i.e, knowing starting hand requirements, knowing your pot odds, knowing your "outs", understanding position, you'll be better than at least 3/4 of the table.
One of the old adages about poker is that you don't have to be the best player at the table to win money, you just can't be the worst. And of course, remember this one... if you haven't figured out in the first 30 minutes who the sucker at the table is, the sucker is you.