jQuery 2.0 would not support Internet Explorer 6, 7 and 8. They would offer a transitional update jQuery 1.9 for developers who want to get the latest features with support for IE.
jQuery 2.0 is scheduled for release early next year just after jQuery 1.9 is made available.
Our goal is for 1.9 and 2.0 to be interchangeable as far as the API set they support. When 2.0 comes out, your decision on which version to choose should be as simple as this: If you need IE 6/7/8 support, choose 1.9; otherwise you can use either 1.9 or 2.0.