many Windows users have the problem to checkout the sources of android, cauz there is no GIT for Windows (although there is one...)
I'll attach the actual sources.
PS: just extract into android-sdk-windows-1.0_r2 folder, so there will be a subfolder sources with android, com, jarjar-rules.txt and overview.html
PSS: using eclipse you can doubleclick the word e.g. Activity and press F3 to get to the source