If you are manually adding and deleting fonts a lot by dragging the files in and out of your fonts folder, font information in the registry can become corrupted. It can also happen if you are using a font manager. Microsoft provides a repair tool for the font folder in the TweakUI utility, which is on the Windows CD and on Microsoft's website.

In some cases, it is necessary to move all fonts out of your fonts folder, delete the registry for your TrueType fonts, recreate the key, and manually re-add the fonts. I don't remember where the key is in Windows XP, but in Windows 2000, it is,

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts

In Windows XP, there is an analogous key for PostScript fonts, since XP offers native support for PostScript.

David