[Source: http://geekswithblogs.net/EltonStoneman]
If there was an announcement, I missed it. But the first CTP is available via an 11-part VM download here:
http://www.microsoft.com/downloads/details.aspx?FamilyID=922b4655-93d0-4476-bda4-94cf5f8d4814&DisplayLang=en#filelist
(if you get a Page Not Found, it's probably a traffic issue. Just have to keep trying…)