I did the promotion in years past. Go here for the full details:
Promotional offer is valid from August 15, 2011 through September 16, 2011 at 11:59 PM PST. You must redeem the Amazon MP3 credit by October 16, 2011 at 11:59 PM PST.
Reminder: You can get Free 2 day Shipping on any purchase when you sign up for Amazon Prime with your .edu account. Here is my post about it.