It turns out to be pretty easy. The only dependency is that you have
to have X Windows installed before you do anything. So
http://ggobi.org/downloads/#mac sez:
"Installing GGobi is a simple three step process:
1. First, make sure you have X11 installed: look in Applications/
Utilities. If it's not there, you'll need to install it from your OS X
DVDs.
2. Next, install Gtk2 (20 meg)
3. And finally, GGobi 2.1.8 itself (5 meg)
On some computers, it takes a very long time to start up the first
time, so please be patient."
After you've done all that, then install R. That is at
http://cran.fhcrc.org/bin/macosx/R-2.8.1.dmg
Finally, start up R and type
install.packages("ctv")
It will ask which CRAN repository you want to use. Pick the one at the
bottom, which is in Seattle.
Then type
library(ctv)
update.views("Graphics")
This takes a while, but it will install everything you need.
Then type
help.start()
This will bring up a browser with links to all the manuals, all of the
packages installed and a search box.