http://www.microsoft.com/windows/window ... nload.aspx
They're not limiting the number of product keys available for general download, so you have about two months to grab a copy. Something noteworthy to mention about the RC and its expiration:
Watch the calendar. The RC will expire on June 1, 2010. Starting on March 1, 2010, your PC will begin shutting down every two hours. Windows will notify you two weeks before the bi-hourly shutdowns start. To avoid interruption, you’ll need to install a non-expired version of Windows before March 1, 2010. You’ll also need to install the programs and data that you want to use. (Learn more about installing Windows.)