In your homedir:
mkdir ~/repodir ~/plugindir ~/eclipse-android
repo init -u git://android.git.kernel.org/platform/manifest.git -b cupcake
The output files are:
~/plugindir/android-eclipse-v200903261355.zip (or whatever date it is)
~/repodir/out/host/linux-x86/sdk/android-sdk_eng.user_linux-x86.zip (replace 'user' with your username)
Not much info about what they do at the moment. Execute the commands in the specified order and it should work. If it doesn't - please comment and I will try to clarify.