Insert the Mac OS X Install DVD (for OS X 10.6 Snow Leopard).
Double-click on Optional Installs to open the folder.
Double-click on Optional Installs.mpkg to launch the installer.
Agree to whatever you're asked to agree to.
At this point, you now have a window listing things that can be optionally installed. They're all initially unchecked. Select "Additional Fonts". Click "Continue".
Alternatively, run the standard installer, but under "Customize" uncheck everything except Additional Fonts. (Couldn't test this, because the optical drive on my Snow Leopard machine no longer works, and I can't get CD/DVD sharing from my Yosemite machine to work.)
