README for installing MacOS version
The Mac version files for NEURON are on the CD at CD:/macinstall/nrn421.hqx
You will also probably want to install the on-line help files, which are provided here in the archive CD:/macinstall/html.hqx
If you want to compile your own new mechanisms, you should read this, and you'll need to install CD:/macinstall/mknrndll/mknrndll.hqx