Kitty,
I'm hesitant of calling people false teachers, and I believe that Osteen geniunely desires to be helpful, but he does NOT preach the gospel. Be very, very, very careful with anything by him. What he says is encouraging, because it is designed to be, but it is not the message of the Bible. Osteen's message is all about how you can help yourself. You can watch videos of him saying with his own lips that he doesn't believe in talking to his congregation about sin. He never uses the word sin. Now when he has one of the biggest congregations in America, something is wrong. It's all very well being encouraging, but if you do not talk about sin you are doing far more damage to your congregation than you are doing good. Sin is our problem, we struggle with it every day of our lives, and that is why we need Jesus. If it's left out, that's not the gospel. It's preaching 'what their itching ears want to hear.'
On top of that, Joel Osteen preaches a prosperity gospel. Put simply, it means if you are a good Christian you will be happy, healthy and rich. That is disgusting. Please don't think I'm saying there is anything wrong with being either of those three things, but they are NOT what God has promised us. He has told us that if we follow him we will suffer. We are living for heaven, and the only way we can live our best life now is if we are going to hell. (I think it was John Piper who said that). That gospel sounds encouraging, because we want it to be so, but it is wrong. Tell that gospel to the thousands of people who die every year because they will not deny the name of Christ their Lord. Tell that gospel to the millions of starving Christians in Africa. Tell that to a Godfearing person whose husband or wife is dying of cancer. Tell that to someone whose child has been killed in a car accident. That gospel draws people to Jesus for the wrong reasons - it is telling people to become Christians so God can do amazing things for them. And when these amazing things don't happen, guess what? People give up Christianity. (The people who preach the prosperity gospel are filthy stinking rich from the money they've raked in from all the people who listen to their 'encouraging' messages.) We must come to Christ because we love him. Simply that. Not because he can do something for us.
Joel Osteen's gospel encourages people to focus on themselves instead of God. If you want solid, biblical preaching, listen to the sermons of someone like John Piper. He sincerely desires the honour of God's name, not his own. He preaches the gospel. Joel Osteen does not. Here's one video from John Piper, which might explain more of what I've been saying:
YouTube - John Piper - Why I abominate the prosperity gospel
Hope that helps!!