I've been practicing playing online (Yahoo) with game money but the betting is very unrealistic. Is there any online or offline software that I can use to practice? I don't have the time nor the money to go to a casino, so that's out.
The differences between online play money and online microstakes cash games are huge. IMO, the microstakes cash NLHE games are similar in nature to a typical $1-$2 NL game in a live poker room. There are some awful players and some that are clearly better than the others, ranging from nitty to loose-aggressive. Deposit a small amount of cash in an online site that serves your geographical area and play in some 1-2 cent or 2-5 cent games. It will help you improve your game much more than the play money route will, and it won't break the bank.
While the differences between fun money and real money online are significant, it does not mean that fun money is not a good place to start. If you cannot learn the skills required to beat the very wild fun money games, you should not move up to real money unless your goal is the life of a degenerate gambler. Your not going to see anything in a fun money game that you are not eventually going to see in a cash game or tournament. You will never achieve optimal play in a cash game if you do not develop a inherent understanding of the very strange and unexpected things that will happen in a fun money game.
The cash games that resemble a fun money game, fast action, people playing with money that seems to have no value to them, are the most profitable games you can master. My casual observation is that most otherwise fine players play these kind of games badly. A little more time and understanding of these kinds of games would greatly increase their bottom lines.
I would urge you not to be so anxious to get away from fun money until you have a significant win rate playing there. Spend a few hundred hours and even after you have graduated to cash games, come back and brush up occasionally.
Poker is not a card game; it is more of a wagering game with cards as props. You will never improve playing with play money and I would say that you will actually become a bad player going down that route. The only way to improve is to start playing online with real money and start learning. Read david sklansky's theory of poker to get some deeper insight into poker.