How do I migrate mypaid AVAST to another, new computer?

MY old machine (windows XP) just flat crapped out (it was nine years old, I can’t blame it). I have a brand new machine running windows 7 home pro. How do I migrate Avast to the new machine? The license file went with the old machine. I am paid up until March of 2013.

Thanks

http://www.avast.com/resend-license-paid.php