After installing ADT, I used SDK Manager to download the source codes for the latest android API. Now when I run the Eclipse version that was provided with the ADT, I still can\
Open SDK Manager-->install source under api(i.e Android 4.0)
if You got No sources attached then click the button, then choose the Directory
e.g: D:\Android\android___sdk\sources\android-17\ ---> this my android sdk location
Depend upon your android installation directory choose accordingly.