tarball: the official .tar.gz package
tarball is the sources itself, not th ebuild
ebuilds are sources packaged in an easy to use gentoo way.
after talking to sLiCeR\ at IRC, he told me there's no way to compile aMuleWeb from the official gentoo ebuild package, so the only thing you can do is compile from the amule.org .tar.gz tarball. sorry
Greetings!