(You'll need a valid Microsoft Live ID account, download and install Microsoft Windows Server 2008 R2 w/SP1 evaluation, and install the Microsoft Private Cloud Beta for free to participate.)

Deal ends after 5,000 registrations. To get your credit:

Sign into or create a Microsoft Live ID account account by clicking here
download & install Windows Server 2008 R2 w/SP1 180-day evaluation and Private Cloud Beta
if prompted, enter coupon code "CLOUD", log in, and learn how to create a private cloud.
your $20 Microsoft Store credit will be emailed to you within three days

Microsoft offers a $20 Microsoft Store credit