1. From the 'Start' menu select 'Control Panel.'
2. Select the 'Appearance and Themes' category.
3. Select 'Fonts' from the 'See Also' panel at the left of this screen.
4. In the Fonts window, select the File menu, and choose 'Install New Font.'
5. Navigate to the folder that contains the fonts you want to install.
6. Select the fonts you want to install. To select more than one font to add, press and hold down the CTRL key, then click the fonts you want.
7. Press the 'OK' button to install the fonts.
   
   View illustrated instructions from Microsoft's website.
   

1. From the 'Control Panel' open the 'Fonts' folder.
2. In the Fonts window, select the File menu, and choose 'Install New Font.'
3. Navigate to the folder that contains the fonts you want to install.
4. To select more than one font to add, press and hold down the CTRL key, then click the fonts you want.
5. Press the 'OK' button to install the fonts.
   
   View illustrated instructions from Microsoft's website.

Fonts can be installed in several folders in OS X, which makes it confusing to new users. We recommend that you do the following:

Drag and drop the fonts into the Fonts folder in your user's Library folder found here:
/Users/Your_Username_Here/Library/Fonts

Using and Managing Fonts in Mac OS X (An official Apple PDF)

Drag and drop the fonts onto the closed System Folder icon.

If you are trying to install Postscript fonts, be sure you have Adobe Type Manager Lite installed as well. Otherwise your fonts will look real jaggy on screen.