The HDMI to Composite or Component is an interesting topic of which I now know more than I ever cared to learn, and this all happened because I wanted to use ATV2 with my Avant.
To begin, for ease of connection I have chosen to use the composite conversion.
You will need to use a convertor box that allows HDMI input with an output of composite. Many audio receivers that are used for surround sound have this feature for the purpose of splitting the sound and signal. If you chose the wrong convertor box you will not get a picture, or you will get a gray scale picture, or something with wavy lines.
Depending on your television you will want to simply convert digital to analog or you might need a downscaler for the television to recognize the signal. For the Avant, I needed to convert the signal to analog and downscale.
There are sets of cables which purport to make these changes by just using the cables alone, but read carefully about their use and success. The reviews in Amazon are very good for a learning base on these cables.