In with the new, and back again

This step-by-step article describes how to add and remove fonts in Windows XP.
If any of the standard fonts that are included with Windows XP are missing, you can run Windows XP Setup again. Setup replaces missing or changed files. If these standard fonts are missing, other Windows XP files may also be missing, and Setup corrects these problems.

Windows supports TrueType fonts or fonts that are specially designed for Windows, and these fonts are available commercially. Some programs also include special fonts that are installed as part of the program installation. Additionally, printers frequently come with TrueType or special Windows fonts.

Tunexp.com:
Install or Remove a font

Also

Microsoft.com/Typography:
Installing TrueType fonts on Windows XP

Bill Reid commented on an earlier post:

"One little known fact about Windows' font handling. You don't necessarily have to move fonts into the Fonts directory to make them usable. If you store extra fonts in another directory, you can double click it, bringing up a dialog that demonstrates the font's usage. If you open your application at this point, it will recognize the font as being installed."