I just bought a new Xbox 360 slim. How can I transfer ALL the data from the old Xbox to the New one?
What about downloaded content that I paid for? Can I re-download it?
Downloadable content should be able to be redownloaded at will, so you shouldn't have any issues there.
For your other content, such as saved games, movies, etc., you have a couple of options:
Once the data is transferred, you will also want to transfer your licenses for content. Instructions are available on the xbox 360 site.