You need a serial number.  I know the following link says for "MAC" but it's the link that allows you to enter your email for them to send you a serial number.  So I would suggest using this link and not going directly to the download page.

http://www.divx.com/dff/index.php?version=mac

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi