http://support.microsoft.com/kb/211916

"Screen Fonts
Microsoft Word is designed to produce WYSIWYG (What You See Is What You Get) output. In order to attain that goal, the text that is displayed on the screen must be able to be printed. If the text is formatted with a screen font, then a font substitution must occur when the document is printed, because screen fonts are for display only and cannot be printed.

A font substitution may produce non-WYSIWYG output. For this reason, screen fonts are not available in the font list.

You can still force Word to use a screen font to display the text by typing the name of the font, exactly as it is named in Windows, into the font list and pressing ENTER."