Update: currently MS has been close the program, so the link is invalid.
https://connect.microsoft.com/site148/Downloads/DownloadDetails.aspx?DownloadID=21028, need join Microsoft Connect project!
current provide the below DDK/WDK
GRMWDK_EN_7600 – WDK for Windows 7
6001.18002 – WDK for Windows Server 2008, Vista Sp1
6000 – WDK for Vista
1830 – DDK for Windows Server 2003 SP1
winddk.rtm.iso – DDK for Windows 2000