IT GENERALLY TAKES AROUND 48 HOURS FOR THE BETA KEY TO BE E-MAILED OUT.

1) Go here
Call of Duty: World at War Beta
2) Fill it in with your email
3) For transaction ID use "XXXXX/01-044" and replace the Xs with numbers
4) Submit and wait

(DO THIS WITH 3 DIFFERENT EMAILS)
One of the emails will get the code

SORRY FOR TITLE I MEANT COD5