ANTLR Downloads takes you to a list of files.
See http://www.antlr.org/wiki/download/attachments/734/antlr3Download.jpg"
Currently you want:
antlr-3.0ea8.tar.gz for ANTLR3
and
antlrworks-1.0ea8.zip for ANTLRWorks the GUI editor.download.html for the latest version.
ANTLR Download directory takes you to a list of files.
There is a mirror of the development source at github