Using Identifont (www.identifont.com) I was able to narrow down the
font to the Garamond family of fonts. I then did some searches to try
and confirm the Garamond font as the one being used by Apple (though
you can see for yourself that they are the same, it doesn't hurt to
have confirmation). I quickly learned that Apple has been using a
custom version of Garamond Narrow for years as their corporate
typeface which they named, appropriately, Apple Garamond.

Here is a brief history of Apple Garamond from MyFonts.com:
"Years ago Apple had used ITC Garamond (Tony Stan, 1977) and
algorithmically condensed it 80% for their corporate typeface. (It is
presumed that the existing ITC Garamond Condensed, at 64%, was too
narrow.) Apple decided at some point to create a true outline to
improve the appearance...Bitstream used its cut of ITC Garamond,
condensed it 80% and adjusted shapes, hairlines, weights, etc. Chuck
Rowe then hinted the TrueTypes using RoyalT, incorporating diagonal
hinting and deltas as well, all to Apple's satisfaction. The fonts
delivered to Apple were known as Apple Garamond."

Bitstream had permission to sell the Apple Garamond typeface under the
name of ITC Garamond Narrow, but as of January 2001 they are no longer
licensed to sell ITC fonts, including Garamond Narrow.

"For all intents and purposes, therefore, ITC Garamond Narrow no
longer exists and the condensed styles provide the nearest
alternative."
http://www.myfonts.com/FontFamily755.html

I then searched the Web for ITC Garamond Narrow, as that appears to be
the font that you wish - despite the claim from Fonts.com that it no
longer exists. I found what appears to be the same font available for
purchase from Adobe:
http://www.adobe.com/type/browser/P/P_1061.jhtml

Other ITC Garamond Fonts are available for purchase through
MyFonts.com:
http://www.myfonts.com/FontFamily755.html

You can also purchase American Garamond from MyFonts.com:
http://www.myfonts.com/FontFamily204.html?refby=identifont

There are several other versions of Garamond available from Bitstream,
including Classical Garamond, Italian Garamond, etc.
http://store.bitstream.com/searchresults.asp?category=&searchtext=garamond&platform=&format=

Garamond #3 is also available from Adobe:
http://www.adobe.com/type/browser/P/P_193.jhtml

Here is the Apple Garamond font available for Mac/Apple computers:
http://www.macparc.ch/nostalgia/applegaramond/

Also, in case you are interested, here is an article on Apple's move
away from using Apple Garamond as their trademark font:
http://www.mired.com/mac/mac_04_29_2002.html

There are some PC versions floating around as well, but since it is a
proprietary Apple font I don't want to point you in the direction of
anything which could be illegal. The other Garamond fonts I listed
above (esp. Garamond Narrow, American Garamond and Garamond #3) are
hopefully all close enough to meet your needs.

Search Terms:
font identification
apple corporate font
"apple garamond" purchase
"apple garamond" buy

I hope this helps to answer your question. Please let me know if I can
be of any further assistance.