The stage 1 of 1.3a_test it's corrupted; tar can't deflate (?) the file stage1-ix86-1.3a.tbz2 PS: Excuse my english ;)
Since many many people already successfully built from stage1, including myself, i think there's just something wrong with your iso/tarball, try redownloading.. Closing..
Moving these so we can remove the "Install CD" component from "Gentoo Linux". I apologize to everyone for this spam, but according to the bugzilla developers, this is the only reasonable way to do this.