Eclipse 3.8 and 4.2 were released concurrently as part of the Juno release, but the compilations for various developer types are only available based on version 4.2.
To use Eclipse 3.8, you will need to download the basic platform and install the plugins you need from Eclipse Marketplace or the Juno repository.
Surf to here and download the one labeled Eclipse SDK:
http://download.eclipse.org/eclipse/downloads/drops/R-3.8.2-201301310800/
Juno repository:
http://download.eclipse.org/releases/juno/