Download
Download the Nominal Isabelle snapshot provided below and
follow the instructions in INSTALL.
Isabelle Snapshot from 7. January 2008 (includes version 0.14 of the nominal datatype package)
INSTALL
Beginning from version 0.13, the nominal package can be started by using
just the command "Isabelle" and enabling the option "HOL-Nominal" in the
ProofGeneral menu "Isabelle -> Logics". If you want that HOL-Nominal is
your default logic, then you can add
ISABELLE_LOGIC="HOL-Nominal"
to the file $HOME/isabelle/etc/settings.