"On Leopard, afaik, niutil is no longer available. You have to use dscl and related commands instead. So,
niutil -readprop / /groups/uucp users
becomes
dsmemberutil checkmembership -U -G uucp
and
sudo niutil -appendprop / /groups/uucp users
becomes
sudo dscl . -append /Groups/uucp GroupMembership
And fixperm.sh doesn't work anymore, since it is build with niutil commands.