To install a font under Mac OS 9 just copy it into the font system folder.
Mac OS X 10.2 and earlier
In the Finder, from the Go menu, select Home.
Double-click the Library folder.
Drag the font or fonts you want to install into the Fonts folder.
Mac OS X 10.3 and later
Locate the font file you wish to install, and double-click the icon. The Font Book will open and display the font so you can see what it looks like.
Click Install Font.
By default, the application installs the font in the Library folder of your home directory, making it available only to you. To make it available to all users on the computer, in the Font Book application, drag the font to the Computer folder in the "Collection" column.